* Adding switch commit to grin outputs
* logging output fix
* adding switch commitment hash to sum tree node
* added hash_with to Hashed trait, to allow for hashing to include another writeable element
* adding hash_with as method in hashed trait
* added global slog instance, changed all logging macro formats to include logger instance
* adding configuration to logging, allowing for multiple log outputs
* updates to test, changes to build docs
* rustfmt
* moving logging functions into util crate
* 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