[3.8] bpo-38738: Fix formatting of True and False. (GH-17083) (GH-17125)

[3.8] bpo-38738: Fix formatting of True and False. (GH-17083) (GH-17125)

* "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>".
(cherry picked from commit 138ccbb02216ca086047c3139857fb44f3dab1f9)