Adding a link in the documentation, moving libsmet to the plugins subdirectory and small fixes in GRIBIO

My previous commit was terrible... it simply made it impossible to define optional keys. This has now been fixed but required a change in the API. So, don't use Config::nothrow but IOUtils::nothrow instead.

In order to try to be closer to the spirit of the STL, now the empty strings/vectors/lists are tested with .empty(), the first/last elements of vectors accessed with front()/back(), the empty strings are not contructed with string("") but with string(), etc This makes a benchmark based on meteo_reading ~4% faster and this makes the code suprisingly easier to read. 

Some extra constification took place as well as some minor code cleanup (optimizing the comparison between two vectors in order to perform less tests, etc).

The Date class can now properly generate and parse full ISO timestamps, including time zone information. The full specification is now supported by convertString() with a helper method in the Date class. Ouputing an ISO string with its time zone is done by requesting the ISO_TZ format.

Some warnings have been fixed in the tests and all 'string tmp=""' or 'tmp=""' have been replaced by either an empty constructor (that does the same ) or tmp.clear() (that does the same too)

The cubic B-spline image resampling algorithm has been implemented in ResamplingAlgorithms2D. Various Weffc++ warnings have been fixed in PNGIO, ImisIO and GRIBIO, leading to the suppression of unused variables.

The plugins are no longer separately loadable libraries, but are fully incorporated into libmeteoio. All classes and facilities that provided capabilites for the dynamic loading were deleted (DynamicLibrary). IOPlugin now holds a function pointer to an instantiation function for children of IOInterface. In IOHandler::registerPlugins() all plugins need to be registered with the key name, the class name, a pointer to an instance of the class and a function pointer to the instantiation function for the class (child of IOInterface). IOInterface lost some complexity and thus the constructor of the base class does not have to be called in derived classes anymore.

The CMakeLists.txt files had to be updated to no longer make separate dynamically loadable libraries for each plugin, but to simply add the classes the user selectes to the meteoio library. 

As a side effect the io.ini key GENERAL::PLUGINPATH is no longer necessary.

Some extra documentation has been added for the UPS coordinate system. The coordinates test has been expanded. A missing default value has been added to the Suntrajectory.

Added some documentation to GRIBIO, fixed the documentation of FilterStdDev, improved the regex for the sun test, significantly improved code coverage by adding lots of different filters and interpolations (both 1D and 2D). The meteo files have been tweaked in order to contain precipitation for the reference time step.

The MeteoData == operator now compares with an epsilon. The chekEpsilonEquality function has been rewritten, according to best practise and inlined. The powN functions have been moved to MathOptim and inlined. This makes the benchmarks 2% faster, that's such a victory...

Since the autotools are obsolete (and unmaintained) in MeteoIO, they have been removed. The popc++ version can be compiled with cmake (with some tricks: disable GSN and force the compiler to popcc). 

For consistency, the various definitions of ot_deg and to_rad have been suppressed and replaced by Cst::to_deg or Cst::to_rad. Some mentions of the Earth's radius have been replaced by Cst::earth_R0. In Coords, some variables have been declared as const.

Outputs that were used for warnings (or information) are now done on cerr instead of cout, in order to avoid poluting the outputs of user code. Should we do the same for the exceptions?

A new method, getSolarTime has been added to SunTrajectory.

A new getMeteo() method has been implemented that transparently performs spatial interpolations and returns a grid for a given parameter. This should be prefered to interpolate(), since it allows the reading plugin to directly provide gridded data (such as coming out of GRIB).
Code cleanup in ResamplingAlgorithms, improved error message in A3DIO. Several keys have been updated/added to the plugins, in order to be more consistent between plugins. Therefore, meteo file extensions are given with METEOEXT, grid2d extensions with GRID2DEXT, grid2d prefix with GRID2DPREFIX (not all plugins support them, though), etc

The usage of SMET for giving special points was not documented. When giving OLWR in SMET, TSS was computed but could lead to an arithmetic exception. PNGIO could throw an exception without freeing all the png_* memory, this has been improved. A few HACKS have been fixed/removed.

Reading data temporal validity was not working for forecast data, that uses more complicated validity model (and I missunderstood how the validity was expressed). This is now fixed and works both on COSMO reanalysis and forecast data (and it is way more complicated and bloated as I ever imagined...).

The wind fields are now all properly corrected for the rotated grid, including U and V. The VW and DW fields are even cached since they might be accessed several times for a given time step.

The geolocalization is now read right after indexing the file and then kept in cache when accessing files by index. The bearing offset required for vector field is now computed and properly applied (except for U and V grids where it is not done yet).

Fixed a naming issue with ARCIO, the cellsize is now computed in a more precise way (using the distance betweens two corners) as recommended by WMO and the distance calculations from Coords are now static methods.

Deleting duplicate points in GRIB was not working properly. The output time zone was not handled correctly in SMET. Some error messages have been improved.

GRIB_PREFIX is now optional, the virtual station lines can now contain comments (useful for giving a location description) and the plugin help text has been improved with some compiling requirements.

A3DIO was not yet working as a true plugin. This should now be fixed. GRIBIO was imposing a "GRIB_EXT" key, it is now optional.

The file extension (or none) can now be specified for GRIBIO. This is necessary for MeteoSwiss files that have no extensions. Better error messages in libsmet (by catching and rethrowing exceptions).

The lat/lon rotation code has been moved to Coords as a static method and some issues have been fixed (it was still not working properly). This should now work and handle correctly the South Pole coordinates as given by the GRIB file (the necessary transformation has been documented in Coords, namely -latitudeSouthPole; 180+longitudeSouthPole).

Some documentation fixes, new gradients (black to white, white to black and blue-white-red) defined and used for new variables in PNGIO (P, ALB and DW). A bug has been fixed for ILWR in GRIBIO as well as a bug when converting geographic coordinates to rotated ones.

New options have been added to the undercatch filter, allowing to specify the temperature thresholds with the CST argument (to make it more similar to GeoTop).

The << operator for Coords has been slightly improved. The Gradient class now generated true-color output when indexed=false (and is used to generate true-color PNGs when PNG_INDEXED=false).

The GRIBIO plugin now reads a file name prefix from io.ini. It also properly convert the internal rotated lat/lon into geographic lat/lon and properly computes cell size. The georeferencing of grids is therefore now correct. The WMO standardized tables are now read first before trying alternate parameters. The documentation has been significantly improved.

The wind velocity for the undercatch correction was taken as is. It is now corrected to 2m using a log profile with a constant roughness length (0.03).

GRIBIO is now able to detect duplicate grid points when associating grid points and user virtual stations, and removes the duplicates (ie: the first station is kept, the other ones leading to the same grid point deleted). This means that before using it, the user should try a simple read_meteo to make sure that his points lead to unique virtual stations.

This version of GRIBIO is able to return meteo data from virtual stations. Some extra checks need to be implemented (for example, ensuring the unicity of the virtual stations). Tested with valgrind for performance and memory leaks.

A read2DGrid(grid, filename) method has been implemented in GRIBIO that returns the first grid it finds. If the input file only contains one grid, this would make sense... The snow height grid is now computed and the albedo grid is now correct (it was in percent). A readMeteo() method has been implemented and is almost functionnal (it just needs to list the available files and extract their timestamp to be finished). Some code cleanup.

Some code cleanup, improved memory management (ie: using the GRIB API free functions). A first version of readMeteo that is not even pre-alpha (therefore de-activated).

In GRIBIO, time range is now checked. Some code cleanup and some parameters are read from another table. The wind height correction has been disabled for now (since we have to standardize what we do here).

Added the wind log scaling law. Code cleanup in GRIBIO as well as more meteofileds supported. The readDEM method has been implemented.

improvements for the Legend class: if the generated legend text is too long, an alternate format is used. Moreover, values close enough to zero are rounded to a true zero.

First working version of GRIBIO!! The file naming scheme might still be non-standard, but it can open a file, index it and access the various fields through the index (ie: it is very fast). When a given field is not available, some backup strategies are tried (like extracting TA and dew point if RH can not be directly read). Specifying a file name as argument does not work however, since such a file is a collection of grids (-> which grid to output?). One option might be to accept it and return the first grid (relevant if the file contains only one grid). A readDEM will be implemented later, as well as the ability to read virtual stations data.

Two new methods have been implemented as static of Coords, to compute the ground length of one degree of latitude or longitude at any given latitude.

A check for 0x0 sized grids has been added to PNGIO. The ability to specify the number of colors (ie: discretization) in the io.ini has been added.

A breakthrough occured with GRIBIO, that starts to be able to do some things. This is still not usable, but definitely moving forward!

A new file has been created to contain math optimizations (fast invSqrt, fast floor, etc). Please keep in mind that you must benchmark your code before committing something using these functions, since such optimizations can actually be slower than the standard version in some cases...

Code updates to GRIBIO (that is far from usable...)

A new plugin appears: GRIBIO, to read GRIB files (see issue 19). This is still extremely preliminary alpha code (enough warnings?!), but it should (hopefully) quickly evolve. A small naming inconsistency has been fixed in template.cc and all plugins now keep a reference to a Config object instead of a full copy (which means that the only full copy of a Config object should now be in IOManager and all other components should have a reference to it).