- introduce Query Context (Qcx) for managing database-per-shard.
- replaces the MultiTx, so mtx.go is retired and removed.
- introduces the HolderConfig struct and all Holders now have
a path from birth.
- rbf speedups on bitwise writes
- badgerdb is removed due to unresolvable write conflicts.
fixes#703#676
- rbf had races around the new rootRecords cache in tx
- rbf tx needed a write lock on the db now that rootRecords are written
- added a global registry for rbfDB to correctly dedup instances
- implement DeleteFragment, DeleteIndex for rbf
- use badger style keys for rbf to allow content checksumming to be list
containers in the same order
- lots of other integration of rbf into pilosa layer.