Add vim modelines to all files.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

library/HTMLPurifier/ConfigSchema/schema/HTML.MaxImgLength.txt

@@ -10,4 +10,5 @@ VERSION: 3.1.1
  This directive is similar to %CSS.MaxImgLength, and both should be
  concurrently edited, although there are
  subtle differences in the input format (the HTML max is an integer).
-</p>
+</p>
+--# vim: et sw=4 sts=4