This implements the IPC binding event for keyboard bindings. It is
slightly different from the i3 implementation [1] since sway supports
more than one non-modifier key in a binding. Thus the json interface has
been changed from:
{
...
"symbol": "t",
...
}
to:
{
...
"symbols": [ "t" ],
...
}
[1] http://i3wm.org/docs/ipc.html#_binding_event
Detects when a bar modifier key is pressed/released and sends a modifier
IPC event to any listeners (usually swaybars).
This way a swaybar can listen on the modifier event and hide/show the
bar accordingly (not implemented yet)
The modifier event looks like this:
{
"change": "pressed", // or released
"modifier": "Mod4"
}
