Adding support for the most recent version of Font Awesome.

As far as I can tell, Hallo does not currently work with Font Awesome 4.0, which changed its syntax. (As detailed here: https://github.com/FortAwesome/Font-Awesome/wiki/Upgrading-from-3.2.1-to-4)

I've gone through and updated the code wherever I saw the old syntax. I think I caught everything, but if not, it should be obvious.