Add unicode support

Just some ideas how to get unicode support in KaTeX.
Seems to work quite well this way.
This isn't unicode, just ASCII =) To get actual unicode, the non-symbol pattern for the Latin blocks is actually `/[\u41-\u5A\u61-\u7A\u8A\u8C\u9A\u9C\u9F\uC0-\uF6\uF8-\u1BF\u1C4-\u24]/`