Subclasses can now be abstract/final, and fixed a bug with :super method

Use the new :abstractExtends and :finalExtends methods to create
abstract/final subclasses.

In addition, fixed a bug wherein a superclass' method that uses :super
inside it would not properly go to said superclass, when itself called
with :super
Bugfix + Indentation fixes

:super now refers to the superclass in the context where the method was
defined, even if it was defined in a superclass
Merge pull request #6 from dvorakroth/master

Fixes to callFromSuperclass + subclasses can now be abstract/final