Add a generic text-prompt system to the Game, and use it to prompt the
character for their name on startup. There's also a Promise type in
util, which is used for the result of the prompt.
Add a new Item raw type and entity type, with preliminary, basic support
for food. There's a really frustrating toml-rs bug that prevents writing
these nicely as toml right now, so I also added support for mixing JSON
and TOML in a single config dir