* Use Zephyr auto CCC discovery instead of doing it ourselves.
* Split service versus characteristic discovery into dedicated
  steps in the flow.
* Fix for not searching properly when connecting to a peripheral
  a second time.

* GATT characteristic allowing passng data + behavior
  label to invoke the behavior on the peripheral side.
* Behaviors have a locality setting to specify where they run.
* Build reset/power/RGB on peripheral.

* Handle disconnects of peripherals, and properly clean up
  and resume discovering for when the peripheral re-appears.

* Make it easier to use *just* event payloads by defining the data,
  and then having event manager macros generate "wrapper structs"
* Improve is_*/cast_* APIs to hide details of full event struct.
* Create `zmk_event_t` typedef to pass to event handlers.
* Bring event names inline w/ consistent `zmk_` prefix.

* Separate header and data struct for the event.
* Remove duplicate struct in split code.

* Avoid deadlocks by using a deadicated workqueue for sending
  position state notifications from peripherals.

* Zephyr BT stack frees TX buffers from system workqueue,
  and to avoid blocking waiting to allocate, perform notify
  from a dedicated queue.

* Avoid corruption by using work to process
  peripheral key position events on the main
  work thread, like local kscan events are.
* Fixes #221

Aligns *.h and *.c to underscore naming convention.

These were kept (with warnings) for backwards compatibility with external boards/shields:
- kscan-mock.h
- matrix-transform.h
They should be removed in the future.

PR: #523