Use matrix encoding for Query.Request.Entropy

@jglidden would you mind reviewing? I'm not sure which order is most appropriate for the pulls

- `support` https://github.com/priorknowledge/loom/pull/75
- `cache-entropy` https://github.com/priorknowledge/loom/pull/76
- `entropy-matrix` https://github.com/priorknowledge/loom/pull/77