Incorrect scoping on Pointer_obj

Now I'm having this issue:

```
Error: ./src/grig/midi/cpp/rtmidi/MidiIn.cpp:331:62: error: no member named 'Pointer_obj' in namespace 'grig::midi::cpp'; did you mean '::cpp::Pointer_obj'?
HXLINE( 71) ::cpp::Pointer< unsigned char > constMessage = cpp::Pointer_obj::fromRaw(message);
```

the cpp::Pointer on the right lacks the :: before the cpp though the one on the left is right. The original haxe code this is from is:

```haxe
var constMessage = ConstPointer.fromRaw(message);
```