* raimo/gen_statem-improvements/OTP-13929:
  Log terminate to sys debug
  Optimize event timeout
  Rework timeout handling
  Clarify the chapter 'Postponing Events' (ERL-284)
  Fix doc and type for state enter calls

typo

Do not start an event timer unless there are no enqueued events.

Handling of timers and timeouts has been cleaned up
and generalized.

Semantic change regarding state timeout zero:

Previously if one state caused a state timeout zero and
managed to stay in the same state to insert additional
timeout zero(s) in the next state callback invocation, then
there would be only one timeout zero event.  The mindset
was that the machine was faster then the timeout zero.

This has changed with the mindset that all state callback
invocations should be independent, so now the machine will
get one state timeout zero event per started state timeout
zero.

Note that just using zero timeouts is fairly esoteric...

* raimo/gen_statem-improvements/OTP-13929:
  Fix race condition in cancel_timer/1
  Use parameterized types
  Implement state timeouts
  Improve docs and types
  Change state entry events into state enter calls
  Improve docs
  Improve docs
  Implement state entry events
  Implement call/3 dirty_timeout