Big update of RGPS product conversion.

A little reshuffling of measures2csv. Still needs an update of the XSL transform. Implemented 'rgps_grid2cell' tool to generate a CSV file that contains grid and cell information. Updated 'rgps2vector' to generate shape files from new flavor CSV files. Rewrote 'measure2netcdf' to create netCDF files in a more generic way. The tool generate GeoTIFF files (plus XML metadata) on the fly. The export to netCDF now works in almost identical fashion as the HDF5 export, using an XML file as input that pulls the various files into one output file.
Merge pull request #308 from rudigens/rgps

Big update of RGPS product conversion.