A section 3 man page should be written to describe libxapian (see the libxml
manpage for example.)

We could also produce debug variants of the libxapian package, built with
--enable-assertions and/or --enable-log (the current -dbg package is just
debug symbols for the libxapian package).

xapian-doc: in index.html, there is one broken link (which occurs in two
places, pointing to the "internal classes" documentation, since we don't
generate this by default).  We could move this to point to the Xapian website.
