bpo-38738: Fix formatting of True and False. (GH-17083)

* "Return true/false" is replaced with "Return ``True``/``False``"
  if the function actually returns a bool.
* Fixed formatting of some True and False literals (now in monospace).
* Replaced "True/False" with "true/false" if it can be not only bool.
* Replaced some 1/0 with True/False if it corresponds the code.
* "Returns <bool>" is replaced with "Return <bool>".
diff --git a/Doc/library/sched.rst b/Doc/library/sched.rst
index fab16f5..a4ba284 100644
--- a/Doc/library/sched.rst
+++ b/Doc/library/sched.rst
@@ -104,7 +104,7 @@
 
 .. method:: scheduler.empty()
 
-   Return true if the event queue is empty.
+   Return ``True`` if the event queue is empty.
 
 
 .. method:: scheduler.run(blocking=True)