Make Merkle tree data store

We would like to store data in a signed chain of blocks, much like git. We have a rather pretty design spec, but we need to implement it. This allows for research replicability, archival data storage, and being respectful of student rights.

This is an awesome project, but it's an essay to write it up.

No source files, tests, or entry points are named. Start by reading the referenced design spec and mapping its requirements onto the repository; the work is done when the specified signed chain-of-blocks data store supports the stated research replicability and archival goals.

Written by the indexing model from the issue text.