Paste computer clipboard to the device on Ctrl+v.
The other direction (pasting the device clipboard to the computer) is
not implemented. It would require a communication channel from the
device to the computer, other than the socket used by the video stream.
We encounter some problems with SDL2_image on MSYS2 (Windows), so
implement our own XPM parsing which does not depend on SDL_image.
The input XPM is considered safe (it's in our source repo), so do not
check XPM format errors. This implies that read_xpm() is not safe to
call on any unsafe input.
Although less straightforward, use SDL_CreateRGBSurfaceFrom() instead of
SDL_CreateRGBSurfaceWithFormatFrom() because it is available with SDL
versions older than 2.0.5.
