Fix documentation organization

The documentation currently lacks organization. It's a bit of a hodge-podge carry-over resulting from the merge of the trac, wiki and other documentation sources.

Here's a shot at a proper structure:

* Getting Started
  * First Steps
  * CMS Examples
* Using WYMeditor
  * About WYMeditor
  * WYMeditor Options
  * Using Skins
  * Using Plugins
* Customing WYMeditor
  * Skinning WYMeditor
  * Examples
  * Tutorials
* WYMeditor Plugins
  * Included Plugins
  * Third Party Plugins
* Plugin Development
  * API
* WYMeditor Development
  * State of Development
  * Brainstorming