Split out JSON Date Converters
This file is pretty large so trying to make more modular. This separates out conversion routines required for getting from the Python space to JSON, but which don't actually serialize the data

Hello @WillAyd! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-01-20 17:16:31 UTC seems like a good refactor.

Out of curiosity, what is the big picture gameplan for the json code? Just trying to make more readable / scalable and learn more about C LGTM cc @jreback can you rebase rebased and green lgtm. thanks @WillAyd 