Implement a concrete "Creature" entity, and place one on the screen at
the game startup for testing.
This revealed a bug with drawing when getting the maximum entity
position, but that appears to be fixed now (yay)
Implement messages almost the same as in the Rust version, only with
YAML instead of TOML this time, and a regular old mustache template
instead of something handrolled. Besides that, pretty much everything
here is the same.
