** New features and improvements: **
* New set of backends added:
- Kitsune
- Mozilla Club
- ReMo
* Backends updated to be compatible with Perceval 0.5, using the namespace
schema and the new implementation of `BackendCommand`.
** Bugs fixed: **
* Offset was not stored in ReMo cache. This caused errors when trying
to resume with items from the cache. (1)