Error code subclasses

http://duktape.org/api.html#defines.3

* [x] Raise error subclass in eval error handler
* [ ] Raise error subclass for "complex objects"
* [ ] Raise error subclass for "unknown objects"
For bad types passed to `prop_call`, I think we should raise a `TypeError`. The generic class is probably fine, but I'm cool with defining a context inherited `TypeError` if you think thats better.