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>

Python/pytime.c

@@ -33,6 +33,7 @@
 /* Conversion from nanoseconds */
 #define NS_TO_MS (1000 * 1000)
 #define NS_TO_US (1000)
+#define NS_TO_100NS (100)
 
 
 static void
@@ -568,6 +569,16 @@ _PyTime_AsNanoseconds(_PyTime_t t)
 }
 
 
+#ifdef MS_WINDOWS
+_PyTime_t
+_PyTime_As100Nanoseconds(_PyTime_t t, _PyTime_round_t round)
+{
+    _PyTime_t ns = pytime_as_nanoseconds(t);
+    return pytime_divide(ns, NS_TO_100NS, round);
+}
+#endif
+
+
 _PyTime_t
 _PyTime_AsMicroseconds(_PyTime_t t, _PyTime_round_t round)
 {