Per application color saturation support (#21)

* Initial implementation without fullscreen support

* Limit saturation to 2

* Fixed saturation not working for fullscreen applications like CSGO

* Fixed saturation ignoring border radius

* Updated README and sway.5 man page

* Rebased from Master

* Added command to README

* Fixed nitpicks

sway/meson.build

@@ -73,6 +73,7 @@ sway_sources = files(
     'commands/mark.c',
     'commands/max_render_time.c',
     'commands/opacity.c',
+    'commands/saturation.c',
     'commands/include.c',
     'commands/input.c',
     'commands/layout.c',