Some unit test cases and stub methods implemented

Lots of code modifications. There are still some stub methods though. It is currently possible to evaluate very simple multiplications and additions (see unit test cases). Many methods have been javadoc'd (except for the unit test cases).
I think the reformatting option in Eclipse has done some weird things with the code, as of gitdiff shows some weirds results. All unit test cases have been evaluated and everything seems to work properly.