support multiple signal_type/observation_code in add_sv_states_rinex #161
Description
Describe the proposed feature
My observation data has multiple signal and observation code, but add_sv_states_rinex prints 'Some ephemeris data is missing'. I have to add the sv states one by one
obs_signal=obs_data.where('gnss_id','gps').where('signal_type','l2').where('observation_code','2X')
sv_states=glp.add_sv_states_rinex(obs_signal)
Motivate the proposed feature
This features make it easier to use in case that multiple GNSS signals need to be considered.