Minor JSON fixes

[mfine]

Improve the python documentation and add to_json and from_json methods to the base SBP object.

/cc @mookerji

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[mfine]

please retest this

[mfine]

retest this please

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[mfine]

This ended up being a catch all for a number of issues impacting the JSON log analysis. It does generate a new set of python files for changes in the generator. It's also skipping the pickle log tests for now.

/cc @fnoble

[mfine]

Towards supporting #110.

[mfine]

Ugh, towards supporting https://github.com/swift-nav/sbp_log_analysis/issues/97.