* Integrate PMMR and its persistent backend with the Chain
* Chain can set tree roots; PMMR backend discard
* Check spent and prune for each input in new block
* Handling of forks by rewinding the state
* More PMMR tests and fixes, mostly around rewind
* Rewrite get_unspent to use the sumtrees, fix remaining compilation issues
* minor cleanup - unused imports
* cleanup build warnings - unused vars
* make structs pub to get rid of the private_in_public lint warning
* missing docs on RangeProof
* add missing docs to store delete function
* cleaned up deprecation warning -
tokio_core -> tokio_io
complete() -> send()
* Beginning work on pool design doc
* Refining data structures; adding connect capability
* Fleshing out the connectivity paths for the tx pool
* Bringing tx pool and orphan set add logic up into parent TransactionPool
* Use output's commitment as identifier in graph structures
* Breaking a bunch of stuff to start migration to output commitment as id instead of hash
* Wrapping up updates to pool using commitment keys, dummy blockchain. Contains lots of cleanup on the internal flow.
* Beginning work on new block reconciliation
* WIP: Replacing monolithic pool cleanup with mark-and-sweep, which greatly simplifies the logic.
* Laying the groundwork for pool tests; test tx generator
* WIP: More elaborate test helpers; starting work on more elaborate block acceptance test.
* Need DummyUtxoSet to actually apply blocks now
* Using search_for_best_output to validate output status in test_basic_pool_add
* Enable modification of chain while under shared pool ownership. Cleanup pending
* WIP: Begining to untangle the TransactionPool impl from Pool and Orphans data structures
* Finishing refactoring of pool block reconciliaition; getting tests working again
* Add metrics for graph sizes; prereq to pool size throttling
* Remove redundant search_for_available_output from pool graph container
* Minimum viable block builder: return all fully rooted txs
* Tests for block building procedure
* Delegate duplicate output checking to check_duplicate_outputs
* Delegate orphan reference resolution to resolve_orphan_refs
