Move to a single page layout

This eliminates the need for all of the HTML pages. It replaces them with a single page `index.html` that uses javascript to load other pages, setting the window history to maintain the use of the back/forward buttons as well as direct link functionality (i.e. you can link someone to `docs.shapeoko.com/#carriages` and it will bring up the carriages page). 

TODO:
- [ ] fix existing internal `.html` links within the documentation. 
- [ ] fix any links on the wiki, etc, or perhaps leave in the old pages and have them redirect to `/`