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/importlib.rst b/Doc/library/importlib.rst
index 54ca8b8..cfde3a4 100644
--- a/Doc/library/importlib.rst
+++ b/Doc/library/importlib.rst
@@ -1168,7 +1168,7 @@
 
    .. method:: is_package(fullname)
 
-      Return true if :attr:`path` appears to be for a package.
+      Return ``True`` if :attr:`path` appears to be for a package.
 
    .. method:: path_stats(path)