SMETIO: Further development of the writeMeteoData procedure. Now all meteo parameters present in the MeteoData objects can be written (so not only the standard ones like MeteoData::TA, MeteoData::RH, etc). This lead to a slight reorganization of the code. Comments were added for private member functions.

GSNIO: More comments explaining the mapping between the GSN meteo data fields and the MeteoData meteo parameters.