Document protocol schema JSON and binary format

[johnstairs]

Documenting the binary format and JSON protocol schema, which is included in the binary and HDF5 formats.

Also making two code changes:

1. The JSON schema for vectors and arrays was not simplifying the representation of a single type (i.e. not a union) to a single value instead of an array with one element.
2. Simplified and made more consistent the code to read and write floating point numbers in the binary format.

[hansenms]

This looks good. If I was to make any comment it would be that at the end of the binary format description, I would actually have and end to end example with simple types and a few datapoints, but maybe we should wait until this has settled down a bit.

[johnstairs]

This looks good. If I was to make any comment it would be that at the end of the binary format description, I would actually have and end to end example with simple types and a few datapoints, but maybe we should wait until this has settled down a bit.

@hansenms Great idea. I've added an example here.