cmd/evm, core/vm, test: refactored VM and core

* 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`.

core/vm/asm.go

@@ -23,6 +23,8 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
+// Dissassemble dissassembles the byte code and returns the string
+// representation (human readable opcodes).
 func Disassemble(script []byte) (asm []string) {
 	pc := new(big.Int)
 	for {