Added the ability for users to specify their own allowed file extensions...

Hi victorproof,

I see that a lot of your feature requests are for adding file extensions, and if the changes are in run.js, they get over-written by future versions of the plug in. By moving this option into .jsbeautifyrc, the changes can be saved through future updates of your plug in, and users can get directly to the options from Sublime Preferences.

It's not quite as versatile as your regular expressions ("sublime-*") but users can get around this by simply specifying the extensions they want supported without using wildcards.

I updated the documentation to mention this change, as well.