Online Custom theme tool

[Chong Yidong <cyd@stupidchicken.com>]

It would be nice to include a variety of user-submitted themes in Emacs
24.  In order to facilitate the process, I hacked together a little web
tool that lets one specify simple Emacs face attributes, preview them,
and submit the result to the Emacs developers.  It's currently hosted on
elpa.gnu.org, at

  http://elpa.gnu.org/themes/

When a user submits a theme, it is saved with a unique URL (which is
just a hash of the theme settings), e.g.

  http://elpa.gnu.org/themes/Cx4QU5wV

This URL can be accessed by anyone, and from that page an Elisp theme
file can be generated.  The submitter's email is also saved to the
server (though never world-visible), so we can contact him/her for a
copyright disclaimer if we want to distribute the theme with Emacs.
Listing of submitted themes is not yet implemented.

The face choices offered by the tool are not very general, because the
primary goal is to encourage users to submit a wide variety of aesthetic
choices for us to pick and refine, not to do the job of M-x
customize-create-theme or manually writing a theme file.

If you like, please play around with this system and help test it out,
and let me know if you see any problems.  Thanks.