Compare the types of expressions and expectations

This is my first try on fixing #12. I've changed the parser slightly so that it also catches the type of the expected value. I've also added a method to the test generator that compares the type of the expression with the type of the expectation (if it is available).

This is still work in progress and I hope to polish it up over the next week, so please don't merge this yet. I just wanted to notify you that I'm working on this. Comments about my changes are also welcome! :smile: