Binary format data migration tool

[ept]

We need a tool to losslessly convert documents in Automerge's current JSON-based format into the new binary format (#253). It will need to do the following:

• In the old format, objects are first created, then linked into the parent. This needs to be converted into a single make operation.
• Transform UUID objectIds into opIds
• Transform per-list elemIds into opIds
• Link operations that arise from undo may need to be converted into operations that re-create the linked subtree?
• Translate dependencies from vector clocks into hashes