change definition of KEEP orientation
create Slot as game concept and corresponding .place() in Card
freeze Yukon, add Klondike using cards.Slots API
make GUI aware of slots
make GUI the owner of game, to allow resizing and decoupling
major reestructure to allow resize
update whole window on resize
post-resize cleanup and refinements on graphics
decouple game rules from resizing
remove dependency on pygame in game rules
refine Klondike init
re-write Yukon rules with new API, using Klondike as base
decouple gamerules from all modules but cards
move Enum class to its own module
add set_theme() method to Deck
fix docstrings typos
decouple cards from g