v0.4.0: Mouse, resize hints and other stuff

This version introduces new config options that people who thinker with the wm may like, window resize hints support (by @onodera-punpun), proper fullscreen support for some programs like firefox (which checks for the _NET_SUPPORTING_WM_CHECK property on the root window before attempting EWMH magic), no more zombie processes and last but not least, mouse support! You can now drag and click windows to move them, focus them, or resize them! (heavily inspired by bspwm)