[racket] ANN: 2048 game - Racket edition

> The big-bang library imposes a lot of overhead to make sure it works well for novice students, and I mean very novice students. So yes, there is a lot of room for improvement here. 
> 
> One day I will have spare time and then I will create a slimed down version of big-bang, little-poof?

Slightly related, is there a version of big-bang that works with typed racket?

Right now it’s giving me this:
. Type Checker: untyped identifier run-it imported from module <2htdp/universe> in: (define (main t) (big-bang ...))
. Type Checker: untyped identifier new-world imported from module <2htdp/universe> in: (define (main t) (big-bang ...))
. Type Checker: untyped identifier world% imported from module <private/world.rkt> in: (define (main t) (big-bang ...))
. Type Checker: untyped identifier proc> imported from module <clauses-spec-aux.rkt> in: (define (main t) (big-bang ...))
. Type Checker: untyped identifier proc> imported from module <clauses-spec-aux.rkt> in: (define (main t) (big-bang ...))
. Type Checker: untyped identifier True imported from module <private/clauses-spec-aux.rkt> in: (define (main t) (big-bang …))