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/hashlib.rst b/Doc/library/hashlib.rst
index 6eb3a7b..b737d22 100644
--- a/Doc/library/hashlib.rst
+++ b/Doc/library/hashlib.rst
@@ -82,8 +82,8 @@
 
 .. versionchanged:: 3.9
    All hashlib constructors take a keyword-only argument *usedforsecurity*
-   with default value *True*. A false value allows the use of insecure and
-   blocked hashing algorithms in restricted environments. *False* indicates
+   with default value ``True``. A false value allows the use of insecure and
+   blocked hashing algorithms in restricted environments. ``False`` indicates
    that the hashing algorithm is not used in a security context, e.g. as a
    non-cryptographic one-way compression function.