Fixed several bugs related to IE8 compatibility.

This is intended to address issue #41

Replaced all instances of .trim() with the regex equivalent (IE8 does not support .trim()).

Added method _getWinSize to accurately retrieve window.innerWidth / window.innerHeight since IE8 does not support such calls.

Added conditional IE stylesheet to the index.html file. Stylesheet must be included after intros.css and provides a proper opacity on the backdrop and a full-white highlight area. IE8 does not support RGBA in CSS.

I tested this using Browserstack.com, and I wasn't able to get the keyboard input working, though I can't tell if this is a real issue or just Browserstack.