Neuronjson Release

Significant changes:

• New neuronjson datatype that is tailored for a small JSON doc (value) for each neuron ID (key). It is a replacement for neuron annotations that had previously been held within keyvalue instances and uses in-memory store for the HEAD version and persists data to chosen backend.
• Upgrade from Badger v2 to v3. This will require you to upgrade your Badger database directories if you have an older version.
• Switch to Go modules from older "go get" install scripts.
• Simplified conda builds and release due to switch to Go modules. (@stuarteberg)
• Support for AWS S3 in the ngprecomputed backend. (Contributed by @pgunn, Flatiron Institute)
• Expanded number of versions for in-memory mapping in labelmap datatype. Limit before was 256 versions, now expanded to uint32.
• Ability to renumber labels in labelmap datatype, as well as keeping track of split or renumbered labels by inserting 0 into in-memory mapping.
• Can now specify Xth parent of a branch leaf using uuid:branch~X for UUID.
• Lots of fixes.