Add in the string-library.

  I'm pretty sure we don't need this Makefile for CLang, but since
 we have it then it should be up to date, and it should work.
  Added new member : files_in_directory.

  This will be useful.
  Use CFile::files_in_directory()

  Now that we have it this is useful.
  Add TODO-entry.
  Load /etc/lumail.d/*.lua on-startup.

  I'm going to move towards expecting to load ~/.lumail.d/ and
 /etc/lumail.d/ rather than the simple paths.

  This makes things easier.
  Create /etc/lumail.d/ in the package.
  Fixed build-dependency upon libglibmm-2.4-dev
  Document /etc/lumail.d/*.lua
  Significant comment updates.
  Updated the sort handling to be consistent.
  Avoid collisions when generating maildir filenames.

  This updates #122.
  Explicitly setup a default sort order.

  ALthough the #121 sounds like it might be a real bug we have no
 proof yet.  Using date-asc is significantly faster than header-asc
 because we only need to stat() the files, not parse them.

  So on that basis I'm leaving this as the default, but will document
 it.

  Updates #121.
  Reverted the test code for #122.
update maildirs after creating a new one
Merge pull request #123 from kain88-de/fix_create_maildir

That's an obvious bug now you've pointed it out.

Merged.

Thank you very much.
  Dump headers too.

  This might help with #124.
  Updated manpage.

  This closes 120.
  Updated the processing of outgoing messages.

  In the past we used to cancel the MIME-fu if we had no outgoing
 attachments.  Now we continue regardless.
  Set the global (boolean) DEBUG appropriately.
 Log the header requested.

  This is part of #124.