Updated to add character flipping

I had a feature request to add the ability to flip the people, since it was a little bit of a bummer that they could never look at each other. You can now do that with the human characters and the stuffed animals by pressing spacebar. Feel free to request other features.

One feature I'd really like to add is a darkness mask, so that fort pieces block out light. I have never done anything like that, so that'll be a longer term learning goal for my free time, which is limited now that the semester has started.

I've also thought about adding the ability to pan up and down, measuring the fort size, and timing the fort building based on breakfast being ready.

Anything you'd like me to add?