* Track active mods when mods or keycode
events occur.
* Use the tracked mods when releasing or
generating keycode events.
* Track pending/used status in one array, for
improved storage efficency.
* Add initial event manager implementation,
roughly mimicking Nordic's API.
* Add `position_state_changed` and
`keycode_state_changed` events.
* Hook up HID and keymap to new events
instead of using behaviour global event
crazy.
* Use extra comptible = "zmk,behavior-global" to add
behaviors to global bindings for event notification.
* Implement mod-tap, as a keymap binding and global one
to skip tap if other keycode pressed while held.
