Read OPDS feeds other than calibre

[steinarb]

Some examples:

• feedbooks:

  http://www.feedbooks.com/books/top.atom?category=FBFIC028000&lang=en
  http://www.feedbooks.com/catalog.atom

• Internet archive:

  http://bookserver.archive.org/catalog/

• Pragmatic bookshelf:

  http://pragprog.com/magazines.opds

• ManyBooks:

  http://www.manybooks.net/opds/index.php

• Project Gutenberg:

  http://m.gutenberg.org/ebooks/?format=opds

• O'Reilly:

  http://opds.oreilly.com/opds/

• Baen ebooks:

  http://www.baenebooks.com/stanza.aspx

[steinarb]

The branch read-feeds-recursively-and-flatten-list contains work in progress on this, from October 2015.

As I recall, I gave up on this because the code to handle the different OPDS variants became more and more messy.