Rename `foldp1` to `foldp'`, I think the previous name suggests different behavior.
Add `foldp1 :: (a -> a -> a) -> Signal a -> Signal a`
Add type hints for all of these functions.
- All basic elements can now be displayed and updated. Updates no longer rebuild the whole scene; instead they only replace as necessary.
- Add `container` primitive which allows people to position Elements in a more flexible way.
- Collages can now handle sprites, textures, and Elements!
Still need to work on making Signal.Input play nice with the new Graphics libs.