Move fragment and vertex shaders to separate file

Through use of a helper function `getSource(url)`, move the fragment and
vertex shaders to separate files.

Note: Need to run the page with a webserver. An easy way for local
testing is to use `python -m SimpleHTTPServer` in the repo directory.

Note2: For glsl syntax highlighting, use: http://www.vim.org/scripts/script.php?script_id=1002