Basic Interpreter capability added, tested using 'say (2 + 2)'
Added print capability to lambdas
Pulled up common frame capabilities into AbstractFrame
Added NativeException for exceptions thrown in JavaLambda's
Exposed Heap#put(Lambda) method in Frame
Heap#put(Lambda) will now check if Lambda already exists before 'putting' it, returns appropriate LambdaReference in both cases
Added MainFrame as starting point for call stack
Shortened equality checks for NullConstant and BooleanConstant