GLR extension for Happy.

GLR parsing allows parsing of ambiguous grammars, to produce a directed,
acyclic, and-or graph which compactly represents possible alternative parses.

This code has been built from scratch and tested on the examples.

Documentation not yet ready - will check in soon

NEW:
 * examples/
    - some examples of using the parser
 * src/ProduceGLRCode.lhs
    - generates the GLR parser from templates and LR tables
 * templates/GLR_{Base,Lib}
    - driver components for the parser

CHANGED:
 * src/GenUtils.lhs and src/ProduceCode.lhs
    - moved mapDollarDollar into GenUtils, and corrected bug on thd3(!)

 * src/Main.lhs
    - new flags added, and call the GLR parser if selected

 * LICENSE
    - added mention of this work.