Generate MsgPack export/import

[leonkunert]

trafficstars

We should try to reimplement the msgPack format from spacy. https://msgpack.org/ should be helpful. Maybe also implement import.

[tecoholic]

I think the current format that spacy uses for NER data is DocBin. I don't know if there is a open spec that will allow reading and writing this format. Maybe reading the spacy code will help.

Either way, I don't see a big need for msgpack.

[leonkunert]

The DocBin format is a gzipped MsgPack https://spacy.io/api/docbin

[tecoholic]

@leonkunert Ah.. I should have RTFD. Thanks for pointing out. Then this is something that should be definitely implemented.

[leonkunert]

The token, spaces and lengths fields can be difficult. They are serialized numpy arrays.