Update src link to toggle between source and text

Currently the Src link in the header will goto the source on the first click, then to a 404 on second click. Changing behavior to toggle between source and the text.

- added src_url method to DocPage and replaced src link href with call to src_url
- override src_url in RawPage to link back to text of page
- add .ruby-version to .gitignore as rvm now uses .ruby-version files