Messagepack file storage format

[jthorton]

We can decrease the size of our dataset.json files further by using something like messagepack it might be worth looking at adding this as a serialisation option.

[mattwthompson]

Are you thinking about dumping it out to JSON and then compressing it down, or serializing to a different format directly?

The closet work I've done to this is in YAMMBS where most of the composition of the JSON files are coordinates where most of the compression options (bytes, other NumPy stuff) aren't JSON compatible. And I think just zipping the JSON file after the fact was clunky for some reason.