Add Scancode and Character handling

[Kylogias]

Adds the HandleScancode and HandleChar functions, for CNFGHandleInput to call for scancodes and characters respectively. They are used in the same way as the other input handling functions, meaning they must be provided for the project to compile. That is, if you are using the Windows and X11 drivers as those are the only drivers where this functionality is currently implemented. The argument for HandleChar is a UTF-8 character. The scancodes should be the same between systems assuming they use the same keyboard drivers (this also means Linux and Windows don't share scancodes)

Adjusted the examples so they will still compile after this change

[cnlohr]

We really can't go this route - it's too painful for users to have to implement another function anywhere this is used. It was a HUGE pain when we added destroy.

What we can do though is make it so from the key press function, we could call the get scan code / get whatever code. Where that information could be stored in a variable.

Instead of making rawdraw -> client calls, can you make client -> rawdraw calls? That doesn't have the same restrictions.

[Kylogias]

Changed the scancode and character output from calling a handling function to checking a global variable inside the handling function, which is (so far) guaranteed to have the correct value for both characters and scancodes. They are set to 0 if there is no character/scancode or if the platform doesn't support it.

[cnlohr]

I think this is all good from my end, let's get at least one other person to sign off on this.