Cleans up the grammar a bunch.
Adds methods in the VirtualMachine for adding and getting property records. Also removes some comments.
Finishes up the implementation of VisitAssignmentExpression, cleans up its tests, and adds a couple more tests for property assignment.
Updates the grammar a bit more. Assignment expressions have been condensed into one AssignmentExpression (rather than Add/Sub/etc).
Finishes (for reals this time) the rest of the implementation for the new and improved VisitAssignmentExpression and adds tests for compound assignment.
Removes a worthless instruction.