Issue #27076: Doc, comment and test function name spelling fixes

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.
diff --git a/Lib/cgi.py b/Lib/cgi.py
index 64ba6d1..7c51b44 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -175,7 +175,7 @@
 
 
 # parse query string function called from urlparse,
-# this is done in order to maintain backward compatiblity.
+# this is done in order to maintain backward compatibility.
 
 def parse_qs(qs, keep_blank_values=0, strict_parsing=0):
     """Parse a query given as a string argument."""