Define variadic functions

[hrs]

Standard Scheme uses a dot notation to define functions that take a varying number of arguments:

(define (my-function (a b . the-rest)
  ...)

We'll need to tell the parser to accept dots and modify lambda and define to handle this.

[hrs]

A side benefit of this is that we'll be able to implement list in the standard library in terms of cons, if we want to.

[hrs]

Fixed in 414f6f8.