Issue #27626: Spelling fixes in docs, comments and internal names

Based on patch by Ville Skyttä.
diff --git a/Tools/demo/redemo.py b/Tools/demo/redemo.py
index b10b030..8335d4c 100755
--- a/Tools/demo/redemo.py
+++ b/Tools/demo/redemo.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 
-"""Basic regular expression demostration facility (Perl style syntax)."""
+"""Basic regular expression demonstration facility (Perl style syntax)."""
 
 from tkinter import *
 import re