Catalog filtering should now be case/diacritics insensitive for all
fields. However it is not validated for language, name and category
fields, and is validated for tags, creator & publisher only for text
supplied in the filter (but not for values read from the book).
Catalog filtering by titles/description was sensitive to diacritics
present in the query string. Fixed that.
Also enhanced the unit test to validate the insensitivity to diacritics
present in either the title/description or the query string.
Now the LibraryTest.filterCheck unit-test validates the actual entries
returned by `Library::filter` (previously only the count of the results
was checked).
The new unit-test fails with a reason not expected before it was
written. The `Library::filter()` operation returns a correct result
after the call to `removeBookById()` (this was a surprise!) but it has
a side-effect of re-adding an empty book with the id still surviving
in the search DB (the emptiness of this re-created book doesn't allow
it to pass the other filtering criteria, which explains why the result
of `Library::filter()` is correct). Had to add a special check
to the new unit-test against that hidden side-effect of
`Library::removeBookById()` + `Library::filter()` combination.
As we use the main library of gtest (if already installed)
we don't need to (and must not) define a main function for the tests.
Does the same (use main library) if we use the subproject.
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.
