Glyphicons copy to clipboard shortcut

This is a relatively simple feature addition for the ability to hover over a glyphicon in the docs and press Cmd/Ctrl+C to automatically copy the ```<span>``` element with the appropriate classes for the icon. It also includes a slightly delayed tooltip to let the user know about the action.

Based heavily on the idea from [Trello](http://stackoverflow.com/questions/17527870/how-does-trello-access-the-users-clipboard) using only JS (no flash) -- uses a hidden ```textarea``` to temporarily copy the contents into and select before the user hits C.

Tested in Chrome 28 for Mac & Windows, Safari 6.0.5 for Mac