* Add client-traits crate
Move the BlockInfo trait to new crate
* New crate `machine`
Contains code extracted from ethcore that defines `Machine`, `Externalities` and other execution related code.
* Use new machine and client-traits crates in ethcore
* Use new crates machine and client-traits instead of ethcore where appropriate
* Fix tests
* Don't re-export so many types from ethcore::client
* Fixing more fallout from removing re-export
* fix test
* More fallout from not re-exporting types
* Add some docs
* cleanup
* import the macro edition style
* Tweak docs
* Add missing import
* remove unused ethabi_derive imports
* Use latest ethabi-contract
* Move many traits from ethcore/client/traits to client-traits crate
Initial version of extracted Engine trait
* Move snapshot related traits to the engine crate (eew)
* Move a few snapshot related types to common_types
Cleanup Executed as exported from machine crate
* fix warning
* Gradually introduce new engine crate: snapshot
* ethcore typechecks with new engine crate
* Sort out types outside ethcore
* Add an EpochVerifier to ethash and use that in Engine.epoch_verifier()
Cleanup
* Document pub members
* Sort out tests
Sort out default impls for EpochVerifier
* Add test-helpers feature and move EngineSigner impl to the right place
* Sort out tests
* Sort out tests and refactor verification types
* Fix missing traits
* More missing traits
Fix Histogram
* Fix tests and cleanup
* cleanup
* Put back needed logger import
* Don't rexport common_types from ethcore/src/client
Don't export ethcore::client::*
* Remove files no longer used
Use types from the engine crate
Explicit exports from engine::engine
* Get rid of itertools
* Move a few more traits from ethcore to client-traits: BlockChainReset, ScheduleInfo, StateClient
* Move ProvingBlockChainClient to client-traits
* Don't re-export ForkChoice and Transition from ethcore
* Address grumbles: sort imports, remove commented out code
* Fix merge resolution error
* merge failure
