No image reloading support

[Darksonn]

I keymap to reload the image, and an option to automatically do so, would be very useful.

[eXeC64]

Note for whoever ends up implementing this:

Use inotify with the IN_CLOSE_WRITE event to know when to try and reload the current image.

This should also have its own subsystem (i.e. C source file and header) to handle watching a file, to wrap it in a nice interface. That way we can keep unnecessary state and logic outside of the main loop.