82 -  CSS style guide

A proposed style guide to cover CSS code commits to the jQuery projects.  Open to suggestion for rules, this pass is based on the CSS in jQuery Mobile and jQuery UI.

Based off of Issue https://github.com/jquery/contribute.jquery.org/issues/82
I covered this in the example, but I should perhaps be a bit more clear in this description.  In this case I meant don't do something like `padding-left: 10px; padding-right: 10px; padding-top: 5px; padding-bottom: 20px`, when you could just write `padding: 5px 10px 20px 10px;`   I can try clear up my language a bit here to try and make it more understandable.