Add example program showing table iteration
Remove Option return value from describe()

All users of describe() seem to be calling .unwrap_or_default(). It's
easier to just define non-valid indexes as returning ~"".
Implement newthread() and atpanic()
Implement the rest of the core API (with the exception of debug)
Implement debug API
Implement the rest of auxlib, with the exception of Buffer
Implement the Buffer methods
Update README