Added Unicode.h and Unicode.cpp. Contains a function for getting a code
point from UTF-8 encoded characters. Added MalformedStringException as an
exception to be thrown if the UTF-8 character passed to the function does
not adhere to the expected format, or if it's too short.

Started support for KeyDown, KeyUp. Renamed KeyPress event to CharacterTyped
and added full support for the event.
Added ability to ignore repeated key down / character typed messages.

Macro utilized for signal declarations in Window.h.

Renamed MouseRelease / MousePress to MouseUp / MouseDown.

Added MouseScrollEvent and Key enum to WindowsEvent.cpp, not used yet.

mainProc forwards message processing to the target window's wndProc now.

Fixed a bug in Window::setVisible caused by an overlooked single-line if that
required you to do setVisible(true) to toggle the window visibility.

Fixed a bug in Window::setVisible that didn't nullify the WindowImpl
pointer after deleting it.

Added .gitignore to VS2013/ to ignore various non-versioned files.