New bookstore: Pragmatic Programmers

[Roberto Alsina]

It turns out that the OPDS code is *almost* generic enough to work well
with many catalogs, so it takes mostly a bit of tweaking to get nice output.

So, here's an experimental one! This is the Pragmatic Programmers store.

* It has free content (their monthly magazine)
* It has paid content (their books), but you get it DRM-free

I am not going to buy a book to test it, though.

If you want to take a look, branch issue5, remember to enable the plugin
first!