function ConsNode(cons, children) {
    this.cons = cons;
    for(var i = 0; i < children.length; i++) {
        this[i] = children[i];
    }
    this.length = children.length;
}
Represents a constructor node

Example: Add(Num("1"), Num("2")) is constucted
   using new ConsNode(new ConsNode("Num", [new StringNode("1")]),
                                        new ConsNode("Num", [new StringNode("2")]))
   or, more briefly:
       tree.cons("Add", [tree.cons("Num", [ast.string("1"), ast.string("2")])])