py: export as python byte array

[pluess]

I added the the possibility to export python code. It's a modified copy of the c export.

Unfortunately I did not manage to read the generated python code again. But I don't know if that's necessary.

ernst@Schamgar ~/Dropbox/Source/python/monobit
[632] : python3 convert.py c64-german.draw c64_german.py
INFO: Loading `c64-german.draw` on `.` as hexdraw
INFO: Saving `c64_german.py` on `.` as Python source.
ernst@Schamgar ~/Dropbox/Source/python/monobit
[635] : python3 convert.py --debug c64_german.py c64_german.c
DEBUG: Opening file `c64_german.py` for mode 'r'.
DEBUG: Exiting <Stream name='c64_german.py' mode='r'> with reference count 0.
DEBUG: Opening DirContainer container `.` for 'r'.
DEBUG: Opening file `c64_german.py` for mode 'r'.
INFO: Loading `c64_german.py` on `.` as Python source
DEBUG: Exiting <Stream name='c64_german.py' mode='r'> with reference count 0.
DEBUG: Exiting <DirContainer name='.' mode='r'> with reference count 0.
ERROR: load_py() missing 1 required keyword-only argument: 'identifier'
Traceback (most recent call last):
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/storage.py", line 63, in open_location
    with open_container(stream, mode, overwrite=overwrite) as container:
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/containers.py", line 45, in open_container
    container_type = _identify_container(file, mode, overwrite)
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/containers.py", line 65, in _identify_container
    raise ContainerFormatError('Expected container format, got non-container stream.')
monobit.containers.ContainerFormatError: Expected container format, got non-container stream.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/ernst/Dropbox/Source/python/monobit/convert.py", line 92, in <module>
    pack = monobit.load(infile, format=args.from_, **loader_args.pick(args))
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/storage.py", line 81, in load
    return _load_from_file(stream, container, format, **kwargs)
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/storage.py", line 90, in _load_from_file
    fonts = loader(instream, where, **kwargs)
  File "/Users/ernst/Dropbox/Source/python/monobit/monobit/scripting.py", line 35, in _scriptable_func
    result = func(*args, **kwargs)
TypeError: load_py() missing 1 required keyword-only argument: 'identifier'
ernst@Schamgar ~/Dropbox/Source/python/monobit