Improved an error message, improved the main documentation page by adding links to the home page, improved the code examples

A new method for getting the parametrized ILWR has been implemented that chose between various parametrizations depending on the available data. The data_converter example has been slightly edited for clarity.

A wrong commit on doc/examples/io.ini has been reverted. A new undercatch filter has been implemented, following (Hamon, 1973). I would not recommend using it for the moment, though. 

The issue 222 was actually more complex than it seemed: the behavior of an uncaught exception is actually not specified by the standard, so there is nothing that could be doneon MeteoIO's side: instead, each application is invited to properly wrap its calls in try/catch blocks, or wrap its whole main in try/catch. The code examples and examples have been modified to show several such possibilities.

Cleaner definition of epsilon in MeteoData. Finally, working 2D_interpolations test (with reference files and relying on numdiff).

Small update to the SMET specs, fixed some stupid bugs in data_converter and added a wind velocity threshold for the Tretyakov undercatch correction (since the fit were done on wind speeds way lower than what Elena had). Such thresholds might generally be required for the undercatch correction...

Bringing up to date the data_converter that fell behind a while ago (for a commented out section of its code).

The autotools' Makefile.in that is necessary for the popc version has been updated. The io.ini and data_converter.cc have been improved (some errors/obsolete keys were in io.ini)

The documentation has been updated (structure diagram, missing key in ImisIO) as well as the code examples so that they use the latest changes.

The documentation and examples have been updated to reflect the latest changes in MeteoIO (namely: the merging of MeteoData with StationData). A documentation bug has been fixed, that involved deleting the doxygen comments for the commented "clone()" method in IOInterface. Since this is not used anywhere and has been commented out for a while, this method has been fully deleted.

Meteo2DInterpolator now has its own << operator for debugging purposes.

The EPSG get and set methods have been added to Coords. The "<<" operator has been redefined for ConfigReader (this is convenient for debugging). The SMETIO plugin has been updated (so that it supports EPSG codes and also to change some column names and improve the foutput formatting). Some documentation has been added and the example data set has been replaced by a data set suitable for the whole Switzerland and in SMET format.

When using A3DIO for writing, the files are now correctly split by years. The OUTPATH user parameter was previously not used, this has been fixed.

In IMISIO, the query size limitation has been removed. 

A data format converter using MeteoIO has been added to the examples.