Add XTCE Support through space_packet_parser library

[ddasilva]

This issue is to track the addition of XTCE support through an optional dependency to the space_packet_parser library (https://github.com/medley56/space_packet_parser).

Support is proposed to be through the from_file('something.xml') method, which returns a custom object that wraps the space_packet_parser module.

[ddasilva]

@medley56 @ehsteve

[medley56]

We discussed either

1. Choosing an XTCE definition and packet data file from space_packet_parser
2. Sending me the CSV definition for a data file in CCSDSPy and having me create an XTCE version

THEN, writing an adapter between the space_packet_parser generator API and the CCSDSPy array output format and comparing the results. Let me know when you need anything from me (e.g. XTCE help).

[ddasilva]

Thanks @medley56 . I won't have time for this for the next 6 weeks until I defend my PhD, but there's always a chance I'll get bored and look for something to do before then.