Move vm into subdir

vm/stackframe.go

@@ -0,0 +1,15 @@
+package vm
+
+type stackFrame struct {
+	previousFunctionIndex    int64
+	previousInstructionIndex int64
+	functionMemory           *memory
+}
+
+func newStackFrame(state *State) *stackFrame {
+	return &stackFrame{
+		previousFunctionIndex:    state.functionIndex,
+		previousInstructionIndex: state.instructionIndex,
+		functionMemory:           newMemory(16),
+	}
+}