Tweak intersphinx links.

This fixes our various links to point to https and use trailing slashes, and
makes our syntax consistent.

Reviewed at https://reviews.reviewboard.org/r/6381/
Fixed typo in example code for AuthBackendHook.

Changed "=" to "==" to compare instead of assign.

Testing Done:
Ran the code in a python script.

Reviewed at https://reviews.reviewboard.org/r/6386/
Add __all__ to reviewboard.extensions.hooks.

The hooks module has a bunch of its own classes, but also imports some stuff
into its namespace (which is then expected to be exposed to the world). This
change adds __all__ to said module in order to clarify what should be exported
(which also makes pyflakes happier).

Testing done:
- Ran pyflakes
- Ran unit tests

Reviewed at https://reviews.reviewboard.org/r/6389/