Tasks for Environment Module

Change the scoping rules to lexical scoping and allow functions refer to themselves.

Finish the GUI and the associated filters for output to an HTML stream and renderer.

Enhance and test the substitute() methods on expressions

Add the idea of looking for inline/compiled functions in objects (implementing an interface say FunctionTable) registered associated with an evaluator.

This would separate the functionality provided in the evaluator and the real activities of the evaluator, making an evaluator object dyamically extensible and retargetable.