* NEW: Support for custom expression evaluators.
[GB.EVAL]
* NEW: You can now inheriting the Expression class to create a custom expression evaluator. You have to reimplement three methods: IsSubr(), that returns if a Gambas subroutine is allowed;
IsIdentifier() that returns if a specific identifier is known; GetValue() that returns the value of an identifier. All other methods you add to the class become your specific subroutine,
provided that you allow it in the IsIdentifier() method.
git-svn-id: svn://localhost/gambas/trunk@7545 867c0c6c-44f3-4631-809d-bfa615b0a4ec
