The lexer variant also uses the string parser eventually (for now).

Also:
* document new_rdata_factory_users[] with an example
* Rename new_rdatafactory_users[] to new_rdata_factory_users[]

Removed the socket.shutdown() before socket.close() again, this seemed to cause some errors with the statistics tests (which we will look into separately)

Discussed on jabber

callable() has been removed in Python 3, but was reintroduced in Python 3.2. This fix (check for isinstance(obj, collections.Callable) should make the test work with 3.1 and older versions of 3.

(acked on jabber)

- reduced a line that was 1 character too long
- flipped order of check with isdigit()
- renamed Token::NUMBER_RANGE to Token::NUMBER_OUT_OF_RANGE