add ability to clear raw keyboard handler

[Justin R. Miller]

Thanks as ever @rsta2. What do you think about adding the ability to clear the raw keyboard handler? I have been using this for some time on my own project and am wondering why it doesn't exist in the library.

void RegisterKeyStatusHandlerRaw (TKeyStatusHandlerRaw *pKeyStatusHandlerRaw,
                                  boolean bMixedMode = FALSE);

void ClearKeyStatusHandlerRaw() { m_pKeyStatusHandlerRaw = 0; }

[Rene Stange]

I added a similar method UnregisterKeyStatusHandlerRaw() on the develop branch. The term "unregister" has been already used somewhere else in Circle, so for being homogeneous. Thanks for the hint!

[Rene Stange]

This feature is in Circle 45.2 now.