Python 3 support for extensions

[hbldh]

Changes in Py3 breaks extension init: http://python3porting.com/cextensions.html#module-initialization

ERROR: Failure: ImportError (/home/hbldh/Repos/b2ac/b2ac/ext/ellipse_fitter.cpython-35m-x86_64-linux-gnu.so: undefined symbol: Py_InitModule3)
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Traceback (most recent call last):
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/site-packages/nose/failure.py", line 39, in runTest
    raise self.exc_val.with_traceback(self.tb)
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/site-packages/nose/loader.py", line 418, in loadTestsFromName
    addr.filename, addr.module)
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/site-packages/nose/importer.py", line 47, in importFromPath
    return self.importFromDir(dir_path, fqname)
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/site-packages/nose/importer.py", line 94, in importFromDir
    mod = load_module(part_fqname, fh, filename, desc)
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/imp.py", line 234, in load_module
    return load_source(name, filename, file)
  File "/home/hbldh/.virtualenvs/b2ac_py3/lib/python3.5/imp.py", line 172, in load_source
    module = _load(spec)
  File "<frozen importlib._bootstrap>", line 693, in _load
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 662, in exec_module
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "/home/hbldh/Repos/b2ac/tests/test_int.py", line 23, in <module>
    import b2ac.ext.ellipse_fitter as fitext
ImportError: /home/hbldh/Repos/b2ac/b2ac/ext/ellipse_fitter.cpython-35m-x86_64-linux-gnu.so: undefined symbol: Py_InitModule3