Is it possible to add these constants to pystray._utils.win32

WM_LBUTTONUP and WM_RBUTTONUP are already there, but can the rest of these be added to pystray._utils.win32 so they are already there for whenever `__on_notify(self, wparam, lparam)` is overwritten?

```python
WM_MOUSEHOVER = 0x0200
WM_LBUTTONDOWN = 0x0201
WM_LBUTTONUP = 0x0202
WM_LBUTTONDBLCLK = 0x0203
WM_RBUTTONDOWN = 0x0204
WM_RBUTTONUP = 0x0205
WM_RBUTTONDBLCLK = 0x0206
```
