Added sample hand-unfolded expansion, for scare purposes

worrying code dupication:

Because you expand on nu_pin_read(), rather than caching its return,
each clamp calls nu_pin_read twice, allocating twice the stack. The
same goes for calling min(__MAX()). typeof and sizeof are called dozens
of times. Also, because of the pointer arithmetic in calling
btn_update, there are dozens of unnecessary *&b-like dereference of
reference of btn.

Since function calls are negligably more expensive than simple memory
access, and equally expensive as those reference-dereference cycles, we
may want to use actual function calls.

just look at the file I added to see the duplication horror.

Also i notice we currently don't send any can packets from the steering
wheel. We just increment / decrement the debounce. We don't use the
faster ++ and -- operators either.