Store ndarrays in compact format

[mverleg]

As described in issue #9

For self-contained, compliant json, the solution will be base-encoding of binary array data.

Current plan:

• Extract binary array buffer
• Gzip compression
• Encode in base 64 or 85

Initial solution was base85, but performance tests show it is 27x slower to encode, so it will probably be changed to base64.

[mverleg]

There's a prototype, but it still needs a lot of test coverage