utility converting string to a safe format

 String::Dirify converts a string (possibly containing high ASCII characters,
 and even HTML) into another, lower-cased, string which can be used as a
 directory name or URL.
 .
 The algorithm is as follows:
  * Each high ASCII character is replaced by its normal equivalent
  * The string is converted to lower case
  * Any HTML (including HTML entities) in the string is removed
  * Any characters which are not (Perl) words, spaces or hyphens, are removed
  * Runs of spaces are converted to the separator character