Added a conversion table
GLAPIConversion.clp: Added classes for argument conversion
Moved the argument conversion rules into a separate file

This make the code far more maintainable
GLAPIArgumentConversion.clp: Added message handlers for code generation
GLAPIArgumentConversion.clp: Overloaded message handlers for generating code

The messages are overloaded in the subclasses of the argument builder class to
provide special functionality for "edge" cases.