ODK 2.0 Documentation Review

I've ported the ODK 2.0 documentation from its old home at opendatakie-dev.cs.washington.edu into the ODK docs repo. This includes modifying the content to the use restructuredText, adjusting the style and content to fit the ODK style guidelines, improving readability, and fixing errrs. Check out the pull request.

If you've used ODK 2.0 at all please take a look and leave a review! Its a big one and we could use all the eyes on it that we can get.