Fixed bug with let not exploding first assignment
Fixed bug with let not exploding first assignment

When a let expression had multiple assignments, only the last one
was properly exploded.

E.g. (let ([n (+ 1 2)] [m 1]) (+ n m) was expanded to

(let ((n (+ 1 2))) (let ((m 5)) ((+ n) m)))

instead of

(let ((n ((+ 1) 2))) (let ((m 5)) ((+ n) m)))

Note the lack of expansion for the n value.

Also added a couple of test cases for expansion of let expressions.

oden-lang/oden,AlbinTheander/oden,oden-lang/oden,AlbinTheander/oden