Js error handling

This primarily updates error handling while parsing. It should now work like the Python version if ```robust_parsing``` is ```true```, meaning it always returns ```bad_data``` if there is something wrong.
I made sure that ```bad_data``` always contains the part of the buffer that has been processed (and discarded).

Furthermore I cleaned up the setup (tests, generation scripts, readme). The tests successfully run now. It should be possible at some point to integrate this in Travis-CI, but there's still work to do for that.

Next on my list: make uint64/int64 work. I think this is now the only real problem left with the JS implementation. (of course there are still a lot of rough edges..)