689 documentation

[arthanson]

Fixes: #689

Converts to use GitHub Pages for documentation instead of read the docs. Unfortunately GitHub Pages only supports markdown not sphinx so the docs and doc-comments need to be converted.

[jnovinger]

Some issues I couldn't leave as line comments:

• Response methods still appear to have ReST syntax docstrings

Sorry about all the ticky-tacky comments--I think that's just the nature of these sort of changes.

[jnovinger]

I also noticed pynetbox.models.dcim.Devices.napalm() is still a thing. I'll file a bug to remove that.

[jnovinger]

Found one new thing and couple of existing things that are closer, but not quite there.