Automatic updating for Chrome, Firefox, Safari

Forget about the webstores. It's too much trouble.

This pull includes a rake task "rake deploy" that generates the extension files and update manifest files and uploads them to a host server. Installed extensions look for the update manifest files, determine that a new version has been released, and allows the user to download the new version (or can do so automatically, depending on their options).

Maintaining the extension at the various web stores is a whole lot more hassle, and it's slower too.