Refactored VM to two separate VMs; std & debug

Standard VM should be about 10x faster than the debug VM. Some error
checking has been removed, all of the log statements and therefor quite
some unnecessary if-statements.

ethvm/debugger.go

@@ -0,0 +1,10 @@
+package ethvm
+
+import "github.com/ethereum/eth-go/ethstate"
+
+type Debugger interface {
+	BreakHook(step int, op OpCode, mem *Memory, stack *Stack, object *ethstate.StateObject) bool
+	StepHook(step int, op OpCode, mem *Memory, stack *Stack, object *ethstate.StateObject) bool
+	BreakPoints() []int64
+	SetCode(byteCode []byte)
+}