Documentation Fixes

This PR adds a bunch of documentation fixes.

 - Cleanup of Welcome message.
 - Fixed bad list in custom effects page.
 - Added latest SharpDoc with lots of formatting fixes for MonoGame.
  - [Support for `<paramref>`](https://github.com/xoofx/SharpDoc/pull/15).
  - [Fixed links for out types](https://github.com/xoofx/SharpDoc/pull/17).
  - [Fixed links to topic pages](https://github.com/xoofx/SharpDoc/pull/14)
  - [Various Markdown conversion fixes](https://github.com/xoofx/SharpDoc/pull/16)