multiple assignment stuff in src/mlisp.lisp



I see the code actually specifies the behavior in cases like this:

> ;; [a,b,c]:[x,y,z] means about the same as a:x, b:y, c:z.  Actually it
> ;; evaluates x,y,z  BEFORE any assignments to a,b,c, hence parallel.

If these are the semantics we want, they're easier to implement than the
left-to-right semantics I was assuming.

But the code apparently doesn't do what it says it does....

              -s