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/dialog.rst b/Doc/library/dialog.rst
index 836f662..dc82a97 100644
--- a/Doc/library/dialog.rst
+++ b/Doc/library/dialog.rst
@@ -73,7 +73,7 @@
 
  | *defaultextension* - default extension to append to file (save dialogs)
 
- | *multiple* - when True, selection of multiple items is allowed
+ | *multiple* - when true, selection of multiple items is allowed
 
 
 **Static factory functions**
@@ -227,4 +227,4 @@
 
 .. seealso::
 
-   Modules :mod:`tkinter.messagebox`, :ref:`tut-files`
\ No newline at end of file
+   Modules :mod:`tkinter.messagebox`, :ref:`tut-files`