The binding event will be triggered when a binding is run as a result of
some a user action. The binding event has the following properties:
change: (str) Currently this will only be "run" but may be expanded in
the future. Included for consistency with other events.
binding: (map) the serialized binding
The "binding" member will have these properties:
input_type: (str) either "keyboard" or "mouse"
input_code: (int) the xcb keycode of the keyboard binding if it was
provided or the mouse button if it is a mouse binding.
symbol: (str) the string representation of the input code
command: (str) the bound command
mods: (list of str) a list of the modifiers that were pressed as string
symbols
fixes#1210
