[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)
diff --git a/Lib/difflib.py b/Lib/difflib.py
index 3de1b3d..5d75643 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1074,7 +1074,7 @@
 
 def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):
     r"""
-    Return 1 for ignorable line: iff `line` is blank or contains a single '#'.
+    Return True for ignorable line: iff `line` is blank or contains a single '#'.
 
     Examples:
 
@@ -1090,7 +1090,7 @@
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
     r"""
-    Return 1 for ignorable character: iff `ch` is a space or tab.
+    Return True for ignorable character: iff `ch` is a space or tab.
 
     Examples:
 
diff --git a/Lib/tkinter/__init__.py b/Lib/tkinter/__init__.py
index 57d5b25..9f0e2e5 100644
--- a/Lib/tkinter/__init__.py
+++ b/Lib/tkinter/__init__.py
@@ -1051,7 +1051,7 @@
         return self.tk.call('winfo', 'class', self._w)
 
     def winfo_colormapfull(self):
-        """Return true if at the last color request the colormap was full."""
+        """Return True if at the last color request the colormap was full."""
         return self.tk.getboolean(
             self.tk.call('winfo', 'colormapfull', self._w))
 
@@ -3224,7 +3224,7 @@
     select_clear = selection_clear
 
     def selection_includes(self, index):
-        """Return 1 if INDEX is part of the selection."""
+        """Return True if INDEX is part of the selection."""
         return self.tk.getboolean(self.tk.call(
             self._w, 'selection', 'includes', index))