TODO
Copyright © 2017 Félicien Pillot <felicien@gnu.org>
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.  This file is offered as-is,
without any warranty.

Until 0.6 version:

 * Add "Deepen" and "Validate" buttons
 * Implement real courses, with exercices and tests
 * Record user's learning (by creating profiles)
