bug#44504: 27.1; feature request: doc-view support for Djvu documents

[Eli Zaretskii]

> Date: Sat, 7 Nov 2020 09:55:04 -0600
> From: "Roland Winkler" <winkler@gnu.org>
> 
> I suggest to add a backend for Djvu documents to doc-view.  (See the
> website http://djvu.sourceforge.net/ describing the Djvu format and
> hosting the DjVuLibre library.)  While I am maintaining djvu.el in
> GNU Elpa, the purpose of this package is to edit Djvu documents.  So
> the relation between djvu.el and doc-view is similar to the relation
> between ps-mode and doc-view.  For users who only want to view Djvu
> documents, the fairly big machinery of djvu.el can be rather
> confusing.
> 
> The command line tool ddjvu from DjVuLibre converts Djvu documents
> to various bitmap formats (pbm, pgm, ppm, pnm, rle, and tiff).
> So I believe this should be sufficient for doc-view.  It is also
> possible to extract the text layer of Djvu documents.

SGTM, thanks.  Patches to this effect are welcome.