Add Love GLSL syntax highlighting

This adds support for Love fragment shaders (GLSL). Basically, it's the highlighting from the awesome `sublime-glsl <https://github.com/euler0/sublime-glsl>`_ repo, with the Love-specific changes and variables and types and such added in. Works well and fixes #8 

**Note:** This is for shaders that are their own files, rather than affecting ones that just exist as strings inside .love files. I'll look into recursive language files, and see if I can easily add that in.