bpo-21302: time.sleep() uses waitable timer on Windows (GH-28483)

On Windows, time.sleep() now uses a waitable timer which has a
resolution of 100 ns (10^-7 sec). Previously, it had a solution of 1
ms (10^-3 sec).

* On Windows, time.sleep() now calls PyErr_CheckSignals() before
  resetting the SIGINT event.
* Add _PyTime_As100Nanoseconds() function.
* Complete and update time.sleep() documentation.

Co-authored-by: Livius <egyszeregy@freemail.hu>