handle overloaded methods

This is a failing unit test for issue #11

It also includes the change to BeanBuilder.java that I have made temporarily for my own project's use, although I'm not really suggesting _that_ be merged, as I'm afraid it might be a pretty hacky and incomplete fix, not sure if it even works right for generics -- just including it anyway for the sake of demonstration (so far my real use case just involves zero-argument methods, so it worked for me).