Updated release procedure

@kenearley @stof @koenpunt

Our S3 experiment is not going to last long. @kenearley has already pointed out some possible awkwardness with it and [GitHub's releases](https://github.com/blog/1547-release-your-software) pretty much makes some of the stuff we're doing unnecessary.

If this lands, the new process for updating a release would look like this:

1. Change the version number in `package.json`
2. Call `grunt prep_release`
3. Commit the `package.json` and `chosen.jquery.json` file changes with a version summary (see 3a43166e0084bec8ab1e8621e2aaa4670514c1ca for an example). 
4. Use GitHub releases to format the release notes and create the tag.
5. Add the release zip to the notes

This PR also includes some changes to the documentation that will reduce the amount of times we need to push to ``gh_pages``. Eventually, I'd like to add the version number back and include a direct link to the zip file on the release ... but GitHub doesn't currently offer a file naming convention that backs us up there.