* only store leaves in rm_log
* cleanup
* commit
* add failing test to cover case where we compact
an already compacted data file
* fix the logic for pruning the data file
* rm_log only contains leaves
prunelist only contains non-leaf subtree roots
* cleanup
* commit
* bitmap impl running in parallel
* rustfmt
* this is better - rewind unremoves outpu pos spent by rewound inputs
* commit
* commit
* pass bitmap around when rewinding
* store and retrieve input bitmap per block from the db
* Replace the RemoveLog with the UTXO set.
* utxo set starting to pass tests
* stuff works...
* split store types out
added some tests to compare the performance of the rm_log and the proposed utxo_set
* pull prune_list out into standalone file
* cleanup, get rid of unused height param
* cleanup and add doc comments
* add support for migrating rm_log to utxo_set
* take snapshot of utxo file during fast sync
implement migration of rm_log -> utxo_set
* rename rewound_copy to snapshot
* fixup pmmr tests to reflect cutoff_pos
* cleanup unused import
* check_compact needs to rewind the utxo_set as appropriate
* fix pool tests
* fixup core tests
* cache block_input_bitmaps via LruCache in store
* cache block header on initial write to db
* rename utxo_set -> leaf_set
and remove references to "spent" in grin_store
* better document the rewind behavior
