Fixed the Makefile not working on any other platforms than Linux by replacing the ".so" file extensions with the $(sharedFileExtension) variable.
Made the Windows graphics context class to follow the new platform-specific class scheme.
Made the Windows window class to follow the new platform-specific class scheme.
Fixed the Linux window class destructor not being virtual.
Moved the isOpen check from the platform specific window::open and window::close to the shared implementation instead.