Compat with python2 is currently broken

[jchillerup]

I can reproduce this ad lib in Python 2.7.6. It works fine in Python 3.

>>> from pythonosc import osc_message_builder, udp_client
>>> msg = osc_message_builder.OscMessageBuilder(address = "/foo")
>>> msg.add_arg("bar")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/pythonosc/osc_message_builder.py", line 69, in add_arg
    if builtin_type == builtins.str:
AttributeError: 'dict' object has no attribute 'str'

And if I try to specify the type directly it goes well at first, but breaks when you want to build the datagram.

>>> msg.add_arg("bar", msg.ARG_TYPE_STRING)
>>> msg.build()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/pythonosc/osc_message_builder.py", line 120, in build
    return osc_message.OscMessage(dgram)
  File "/usr/lib/python2.7/site-packages/pythonosc/osc_message.py", line 22, in __init__
    self._parse_datagram()
  File "/usr/lib/python2.7/site-packages/pythonosc/osc_message.py", line 56, in _parse_datagram
    raise ParseError('Found incorrect datagram, ignoring it', pe)
pythonosc.osc_message.ParseError: ('Found incorrect datagram, ignoring it', ParseError('Could not parse datagram string index out of range',))

[attwad]

Yes, as the description and the setup metadata on pypi of this project states, it is aimed at python 3, and all unit tests are done for python 3. I do not plan on adding python 2 support, feel free to fork this repo if you need it.