update TODO
add support for double decks
do not snap when dragging a card
allow per-snap and per-slot overlap values
improve Slot API
fix card flip on restarts
parametization and subclassing FTW!
more functions to Slots API: logical move and drawing
use the new slot API in GUI
all cards have a slot. No more headslot() insanity!
improve Card API a bit more, and use it in rules
add set up for a new: Backbone
Backbone rules completed