Load & parse /etc/mime.types if present.

  This updates issue #46.
  Only load MIME-types once per run.

  The map of suffixes->types is now static, so it is only loaded once
 per execution run.

  We've also added debugging details about MIME-type lookups.

  Closes #46 / Fixes #46.
  Build-Depend upon libpcre++-dev
  Preparing for 0.09 release.
  Mention the new prompt_chars() primitive:

    http://lumail.org/lua/prompt_chars.html