Add IO for RINEX Navigation and Observation files

[ajahraus]

Hey, I love your simulator!

I have a use case where we'd like to create RINEX files from a simulation. The simulation should be based off of actual RIXEX files, and we would like to make changes to induce particular faults to test our fault mitigation algorithms (i.e. modify the RINEX observation file to simulate troposphere delays, or ionosphere delays, etc).

Would you consider adding IO functionality to read RINEX Navigation and Observation files data to establish the Simulator's state, and perhaps also adding the ability to create new simulated RINEX Navigation/Observation files from the Simulation?