Changing name of publicly accessible global values

* midiLabel -> midiLabelPrefix
* midiLabelEvents -> midiLabelCallbacks
Adding shortcut methods for getting the last midi in event value

* you can now do midi.Event() and midi.Values()
* renamed base method to LastMidiInEvent() since nobody will ever use that directly
Refactoring to support multiple devices and menu selection feature

* moved the device open and close methods outside the class, so that they also work when accessed via non-oo means
* moved all class properties outside the class as well
* the class now access as a convenient way to get at everything and help automatically init and destroy, so it is still useful to have
* because of the above refactoring, we can now support opening multiple devices at the same time
* we are also able to support autohotkey menus, so we can supply a checkbox menu in the tray icon that lets you select midi devices via the gui