* refactor externalities::ret to take self by-value, add GasLeft enum, and alter evm::Result.
* remove unused imports, StopExecutionWithGasLeft variant
* adjust tests
* remove extraneous call to reserve
* update json_tests Ext to match new trait
* adjust executive json_test
* have evms own their memory for their entire lifetime
* make finalize API more friendly
* indentation fix
[ci skip]