Added various features

- Added eroded blocks
- Added falling blocks
- Added blocks that kill the player
- Added platforms that are solid for a short while after a button press
- Added edible blocks
- - Added "bouncing block" (jump on it and jump higher)
- - Added "floating block" (solid block that moves up continually as far
as it can)
- - Added "speed block" (non-solid block that launches the player in
their current direction at higher speed)
- Added a dummy "spacebar" object for the tutorial
- Updated the tutorial level (world 1) to reflect the new additions.