cefpython draw fails on windows

[hugohadfield]

See https://github.com/pygae/clifford/issues/85 Example error message:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "E:\projects\pyganja\pyganja\script_api.py", line 237, in draw
    render_scene_string_appropriately(str(sc))
  File "E:\projects\pyganja\pyganja\script_api.py", line 223, in render_scene_string_appropriately
    render_cef_script(scene_string, sig=sig, grid=grid, scale=scale, gl=gl)
  File "E:\projects\pyganja\pyganja\script_api.py", line 185, in render_cef_script
    p.start()
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\popen_spawn_win32.py", line 65, in __init__
    reduction.dump(process_obj, to_child)
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'render_cef_script.<locals>.render_script'
>>> Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\spawn.py", line 105, in spawn_main
    exitcode = _main(fd)
  File "E:\Miniconda3\envs\py3\lib\multiprocessing\spawn.py", line 115, in _main
    self = reduction.pickle.load(from_parent)
EOFError: Ran out of input