Added custom theme for the documentation.

The theme is based on [Hangulize](https://github.com/sublee/sublee-sphinx-themes), by Heungsub Lee, and has its own submodule hosted on GitHub.

There have also been many changes to the sphinx configuration and the `.rst` source files to accomodate the changes. Hopefully the current state serves as enough of a basis for the future.

Signed-off-by: Atheriel <atheriel@gmail.com>