The GSN_URL key is now mandatory and the GSN_USER and GSN_PASS are now optional (for publicly accessible sensors)

A little more cleanup (constification, mostly) in GSNIO as well as documentation. Updated the example io.ini. And a new data generator: Brutsaert for clear sky ILWR.

Small cleanup in GSNIO, changing URL/USER/PASS to GSN_URL/GSN_USER/GSN_PASS. Updated the documentation version; fixed a documentation bug.

GSNIO: Missing NULL values and missing fields and units keys in the header have been fixed on the GSN server side. Plugin updated accordingly.

GSNIO: Now we can deal with offsets and multipliers, which are sometimes indicated in a UTF8 string after the fields definition in the header. The units are given as "°C" or "%" for instance. Thus we can perform a calculation to MKSA. 

GSNIO: Cosmetic adjustments. If the user requested station does not exist, there will be an exception thrown. Otherwise the most pressing issue remains the NULL values in GSN.

GSNIO: reading of meteo data works now. However there are the usual GSN issues, which are plentiful and painful:
1) Big problem: NULL values seem to actually come as 0 values
2) parameter naming conventions: totally inconsistent, also one station might have more than one sensor for a parameter, which one to use?
3) Slow, impossible to retrieve meta data for one station only, meta data formatted in obscure way -> necessary to guess where the timestamp is (current guess position 1 or 2 in the csv formatted data row).

GSNIO: reading of StationData now works perfectly,although terribly slow, due to the fact that it is not possible to retrieve meta data for a selected number of stations only.

Deleting old GSNIO plugin based on SOAP messages and adding new framework based on REST API and libcurl (gnutls variant).

The cmake files for compiling with LibXML++ have been updated since they would not work with more recent Linux (but we should consider dropping LibXML++ and only rely on LibXML2 in order to reduce the dependencies and package finding mess). The special points are now called POI (Points of Interest, like for a gps device) in order to make them more familiar.

Fixing some warnings for Visual C++ and also using ostringstream instead of stringstream when appropriate

More size_t fixes (ie trying to be consistent) and a bug was found when spatially interpolating using a few specific algorithms that would not reset their internal vectors between two calls (thanks Matteo for helping uncover this bug!)

the parameters mapping has been extended to cover access to the imis stations through GSN. Some units thransforms were not being performs.

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)

some code cleanup in GSNIO, the warnings generated by soap are now turned off (with a hack to make old versions of gcc able to do it) and the plugins directory and component are now removed from the packaging

The Date class has been revereted in order to compute year, month, day, etc since this is useful when debugging. The external includes that are used for the plugins are now included as system headers in order to avoid generating warnings for some code that we are not responsible for.

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.

New warnings have been tried to detect variable shadowing (one variable declared with the same name as another one), alignement issues, etc. This produces very verbose output (not all warnings are legitimate) but allowed to fix lots of cases of misalignement and shadowing issues. These options have been left in the CMakeLists but NOT enabled (since these warnings are not so easy to interpret).

The Passive_T filter has been reworked and renamed as ProcPassiveT. A proper documentation has been written for it.

All the cout have been replaced by cerr in order to avoid messing with the end user's application. Some old commented out code has been removed.

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.

This addresses the 2D part of issue 168: the ability to specify which meteo parameter and time step to read/write from/to a 2D grid. This should be the prefered reading method in the future, since it leaves to the plugin the task of building the file name, extension, database table, etc This also provides added metadata and more control over the writing process.

A lot of writes were using std::endl for end of line, which forces a buffer flush. This lead to a visible performance cost (as shown by the profiling project made in collaboration with HES_SO). These have been replaced by "\n" that lets ostream manage its buffer as it wants.