Now the search results page is presented by the backend in the language
controlled by the value of the `userlang` URL query parameter (or, if
the latter is missing, the value of the `Accept-Language:` HTTP header).
Note that the front-end doesn't yet take advantage of this
functionality.
By moving the nameMapper/library arguments in `getHtml`/`getXml` we avoid
any potential "use after free" of name mapper or library as they are not
stored.
We have to reuse the query the user give us to generate the
pagination links.
At search result rendering step we don't have access to the query object.
The best place to know which arguments are used to select books
(and so which arguments to keep in the pagination links) is when we
parse the query to select books.
Fix tests (pagination links) with book selector other than "books.id="
(pattern=jazz&books.query.lang=eng)
Introduces a new member mp_search that houses the zim::Search object,
adds a new constructor for this purpose. This commit also add an
overload for getHtml that takes start and end integers as arguments
since they are not part of the search object we include.