Get the download URL automatically.
Show a spinner while fetching the latest release.
Don't wait for the rest of the page before showing the spinner.
Find the most recent release.
Default to `rake site`

I've started running `rake serve` in one window, and running `rake` when I
make changes.
Add an 'All Releases' button that's always available.
Merge remote-tracking branch 'origin/master' into releases

Conflicts:
	_includes/download_button.html
Merge pull request #2 from git-tfs/js-release-button

Automatically update the release button