Despite the fact that RBTools provides APIs for talking to Review Board

and implementing custom commands and clients, we haven't documented the

codebase publicly.
This adds a code reference to the documentation's API section, and fixes

some syntax errors in the docs that were found during generation. We're

now using Sphinx 5.0, and beanbag-docutils 2.0, to build the

documentation.
There's a lot that needs to be done to clean up documentation in the

codebase, but that's work that can be done over time.

Built the docs. There are still warnings, but they'd require more

extensive work.