Created a generic function multipleQuery which takes:
1. string (representing a comma separated list)
2. param (the value to query on using Xapian).
Category and language query will use this function.
From now on, the `lang` parameter of the /catalog/search,
/catalog/v2/entries, and /catalog/v2/partial_entries endpoints is
interpreted as a comma-separated list of languages.
libzim's search is not thread safe (mainly because xapian is not).
So we must protect our search objects from multi thread calls.
The best way to do this is to associate a mutex to the `zim::Searcher`
and lock the searcher each time we access object derivated from the
searcher (search, results, iterator, ...)
Library became thread-safe with the exception of `getBookById()`
and `getBookByPath()` methods - thread safety in those accessors is
rendered meaningless by their return type (they return a reference
to a book which can be removed any time later by another thread).
Introducing a mutex in `Library` necessitates manually implementing the
move constructor and assignment operator. It's better to still delegate
that work to the compiler to eliminate any possibility of bugs when new
data members are added to `Library`. The trick is to move the data into
an auxiliary class `LibraryBase` and derive `Library` from it.
The search text in the catalog query is interpreted as partial by
default, but partial query mode can be disabled in C++. The latter
possibility is not exposed via the /catalog/search kiwix-serve endpoint,
though.
1. Get the subset of books matching the q (title/description) parameter
of the search
2. Filter out books not matching the other parameters of the search.
Stage 1. currently works in the old way, but will be replaced by Xapian
based search in subsequent commits.
The default value of this parameter is false, in this case all the bookmarks
are returned, otherwise only those who are related to books of the library.
Instead of having a single method `listBooksIds` that tries to be
exhaustive about all the filter and sort option, split the method in
two separated methods `filter` and `sort`.
The `filter` method takes a `Filter` object that represent on what we are
filtering. This object has to be construct before calling `filter`.
```cpp
Filter filter;
filter.query("Astring");
filter.acceptTags({"nopic"});
// return all book in eng and with "Astring" in the tile or description".
library.filter(filter);
//equivalent to
library.listBooksIds(ALL, UNSORTED, "Astring", "", "", "", {"nopic"});
// or better
library.filter(Filter().query("Astring").acceptTags({"nopic"}));
```
The method `listBooksIds` has been marked as deprecated.
Add a small test on the library.
The library now contains (simple) methods to handle bookmarks.
The bookmark are stored in a separate xml file.
Bookmark are mainly a couple (`zimId`, `articleUrl`).
However, in the xml we store a bit more data :
- The article's title (for display)
- The book's title, lang and date (for potential update of zim files)
Nikhil Tanwar
Veloman Yunkan
Matthieu Gautier
Maneesh P M
luddens