* change gas cost for contract creating txs
* invalidate signature with s value greater than secp256k1 N / 2
* OOG contract creation if not enough gas to store code
* new difficulty adjustment algorithm
* new DELEGATECALL op code
* Moved `vm.Transfer` to `core` package and changed execution to call
`env.Transfer` instead of `core.Transfer` directly.
* core/vm: byte code VM moved to jump table instead of switch
* Moved `vm.Transfer` to `core` package and changed execution to call
`env.Transfer` instead of `core.Transfer` directly.
* Byte code VM now shares the same code as the JITVM
* Renamed Context to Contract
* Changed initialiser of state transition & unexported methods
* Removed the Execution object and refactor `Call`, `CallCode` &
`Create` in to their own functions instead of being methods.
* Removed the hard dep on the state for the VM. The VM now
depends on a Database interface returned by the environment. In the
process the core now depends less on the statedb by usage of the env
* Moved `Log` from package `core/state` to package `core/vm`.
