So... I just released version 1.1.0.
The major new feature is that you can now manage collections with calibre! 
A bit more information about the calibre support:
- synchronizing with calibre will never delete any collections, or change the visibility status of any existing item.
 
- synchronization might create new collections, which are visible in Home by default.
 
- synchronization will modify the affected collections, adding or removing items as required.
 
In addition, a few minor changes concern the delete behaviour: deletion is now enabled for multiple collections, and they don't need to be empty before being deleted.