GLSL syntax library

Copperbox revision 454.

I've changed the syntax tree to use Data.Seq rather than lists, Seq allows snoc-ing (adding to the right), so this means that I can take out the revlist productions from the parser (which only reversed a backwards list). This gets the parser back to being almost identical to the grammar.

Also I've filled out the pretty printer so all the datatypes have a corresponding Pretty instance.