Meteo instrument from Dirk

Patch posted by Dirk that implements MDA sentence and a temperature/pressure instrument in the dashboard.
According to http://www.nmea.org/Assets/100108_nmea_0183_sentences_not_recommended_for_new_designs.pdf it's obsolete and vendors should use XDR instead, but I have not found any documented implementation of it so far...
Anybody sees a problem if we merge it?