TODO

 * Valhalla
     -> Improve the log system to send the messages in a callback
        instead of the stderr (if the callback is defined).
     -> Add a public function to provide the ability to send all threads
        in waiting list (pause). Like the ondemand but with the scanner
        too.

 * Database
     -> When files are downloaded and the reference on this file is no longer
        available in the DB, the file must be removed (covers, etc, ...).
     -> Add a public function to retrieve the number of records in the tables
        according to some conditions.

 * Grabber
     -> TheMovieDB grabber is broken; the old API v2.1 is no longer supported
        and the new API v3 is working with JSON instead of XML. It needs to
        implement the JSON parser first.
     -> Allocine and IMDB grabbers are broken; no real webservice.
     -> Add the possibility to configure every grabber at the init. Some
        grabbers can handle several languages and english is hardcoded or
        the language is ignored.
        \see Amazon, TVDB, TVRage and Allocine (french only)

 * Scanner
     -> Add optional support for inotify.
     -> Implement a system to add filters (to ignore some directories)
        for a path.
     -> Add the possibility to keep the files in the database for a path even
        if these files are not reachable. Useful for example with the network
        shares. In this case, it should be the role of the application using
        libvalhalla, to ack the library that the files are now available and
        a new scanning must be performed.

 * Ondemand
     -> Add the capability to force an ondemand for files where the mtime has
        not changed.