v1.3.1 - reimplement COROUTINE_DELAY_MICROS() and COROUTINE_DELAY_SECONDS()

• 1.3.1 (2021-06-02)
  • Bring back COROUTINE_DELAY_MICROS() and `COROUTINE_DELAY_SECONDS(),
    with an alternate implemenation that increases flash and static memory
    only if they are used.
    • The Coroutine itself knows whether it is delaying in units of
      milliseconds, microseconds, or seconds, based on its continuation
      point.
    • Make CoroutineScheduler::runCoroutine() always call into
      Coroutine::runCoroutine() when the Coroutine::mStatus is delaying,
      instead of preemptively trying to figure out if the delay has expired.
    • Coroutine does not need a runtime mDelayType descriminator.
    • The result is that the code to support COROUTINE_DELAY_MICROS() and
      COROUTINE_DELAY_SECONDS() is not pulled into the program if they are
      not used.