addition of null
Almost done with Code Emitting!

Finished classes
Fixed bug where emitted type was %class_[...], but the expected type was %Class_[...]
Fixed bug where type-checker would allow default constructor even if the super-constructor was not trivial.
Implemented "Non Typechecked Upcasts", such as those found in super-method calls.
FIXED HUGE BUG: typeEql() equality check only compared arrayNesting values of element a and b, rather than their typeKey too!