Using proper `world`
Making nicer the code for setting patch variables
Adding type signatures for new methods

I always enjoy doing this, for a number of reasons--not the least of
which being that it exposes insanity.
Fixing up `Prims.member`
Very minor comment tweak
Fixing up `Prims.position`
Fixing up `Prims.remove`
Fixing up `Prims.removeItem`