The HumanReadableId can contains special char (`&`/`=`/...)
As it is used as to create a url in the opds template,
we must url encode it.
- We don't need to encode the book id as it is a uuid, it never contains
special char.
- We don't need to encode the book url as it is read from the library and
the url must already be correctly encoded in the library.xml.
(tests modified accordingly)
