Allow nb converter func to be passed to staged/execution methods

This allows for text-based notebooks to be staged, then converted on the fly before execution (e.g. using jupytext)

Initial Release

Add RTD Documentation (#35)

Also:

* Move tabulate records code to standalone functions (fixes #27)
* Move `get_cache`  to top level and `cli/utils.py` to `utils.py` (improves access and fixes #29)
* Create .readthedocs.yml
* Add PyPi deployment

Initial PyPi release

v0.1.0a1

Add PyPi deployment