Update build params for better navigation and to use sphinx_rtd_theme

[zed-eiq]

Updated .readthedocs.yaml to:

• Use more explicit build parameters
• explicitly use 'dirhtml' as output for pretty urls

Updated conf.py to:

• include 'sphinx_rtd_theme' and 'readthedocs-sphinx-search' extensions, which were already included in docs/requirements.txt
• set theme to 'sphinx_rtd_theme'
• replace html config with sphinx_rtd_theme config

What this means:

• automatically populate sidebar instead of explicitly populating it
• sidebar should now contain all docs. now, you can navigate the docs through that instead of having to navigate almost exclusively through the 'next' and 'previous' buttons

[zed-eiq]

interrogate has a bug where --fail-under always fails when using a float: github[.]com/econchick/interrogate/issues/114

[arcsector]

Been waiting for this to happen - Alabaster is a pain, and i cant believe it's the default. Bravo, gentlemen.

[arcsector]

Wow... The improvement here is staggering... Amazing work getting this out!