support OMM object format

[timotejroiko]

Hello,

celestrak and spacetrack are deprecating the old TLE format in favor of the new OMM keywords in CSV/XML/JSON formats, due to the limited 5 digit catalog numbering in TLE.

It would be nice to have an additional input function with which we could initialize a satrec from an OMM json object instead of a TLE, and would help future proof this library.

Here's the format specification:

https://www.nasa.gov/wp-content/uploads/2017/12/orbit_data_messages.pdf

[joshuarrrrr]

There is already a merge request #122 for that feature but it hasn't been merged yet. I can't tell you why but I'd love to see that functionality as well.