Introduce rbtools documentation

Create the configuration for the rbtools documentation and introduce
the initial documentation for the rbtools api client. This
documentation includes a small tutorial, a general overview, and
resource specific functionality.

Reviewed at http://reviews.reviewboard.org/r/3296/
Add documentation for the rbt commands

A page for each command has been added listing a short description and
the options which the command accepts. Eventually these should be
expanded to provide more in depth documentation.

Also, the post-review documentation has been ported from the Review
Board code base. This also served as the starting point for the rbt
post command's documentation.

Additionally, a couple of unused options, which were noticed while
documenting, were removed from the post command.

http://reviews.reviewboard.org/r/3931/