Make repo more portable

I've made two minor commits:

1) Changes the jquery path to be relative. I'm developing on this project in a subfolder http://localhost/path/to/facebook-slideout/ and the path should be relative to accomodate these situations.

2) Since there's no actual PHP code in the index file, I changed the extension. This means you won't even need any sort of server to play this code.

Thanks for considering these changes!