This adds a number of modules to the Review Board 3.x codebase docs,

helping to find useful and important modules when working with the

product.
This still leaves out a number of modules, mainly those that are more

internal and less useful to expose to third-parties, though it's a fine

line at times.
Some of the module sections now link to the Djblets docs as well,

helping people get a more complete picture of the various parts.
There are also docstring fixes for some modules that weren't previously

included and now break. These modules are still largely using legacy

docstring formats, though. Only the docstrings containing errors were

updated.

Built the docs. Checked for errors and bad links.