Core changes, replace animation system, two new sample games

[ZBlocker655]

Here's a large bundle of changes I've been working on in my fork, in case you would like to have them, too. I'll try to list them succinctly:

Incorporate earlier pull request from @apinkney97

I incorporated an earlier pull request to alter the way controllers are instantiated, which also allows for nicer declarations of controller fields.

Changes to card holders

These are generally breaking changes.

• Fix bug - last_card_callback now invoked in all cases.
• is_clicked now returns true if any card in the holder is clicked. New is_top_card_clicked method to test just the top card.
• sort_cards can accept override sorting scheme.
• Stop using card_sprite to control whether a card is "clicked" or not. Instead, move this logic to a much higher level - into CardsHolder and the sub-class GrabbedCardsHolder.
• Remove all the check_mouse and sprite.clicked logic, so that there is now only one way to "grab" cards out of a holder.

New animation system

I replaced the old Controller.moves collection with a Controller.animations collection accompanied by the new animation.py module. See README.md. The new example games make use of all the new animation logic.

I added animation of cards for Klondike.

New sample games

Created new sample games War and Crazy 8s that showcase the following:

• Playing against a very limited computer opponent.
• Pulsing the background color.
• The line-to-spiral animation (Crazy 8s - try playing an 8.)

[ZBlocker655]

I like those future suggestions! I haven't done type hints yet, but it looks like a really good idea. I'd be happy to contribute more as well.