n-ary lambdas / rest args

[eigenhombre]

I've gotten pretty far without 'em,

But we're gonna want 'em.

• Support dotted pairs - parsing, cons/car/cdr, evaluation, printing, ...
• Adapt dotted pairs to lambdas, e.g. (lambda (x . xs) (list x xs))
• Implement rest-only signature, e.g. (lambda (() . xs) (len xs))
• Implement defn similarly to the above lambda exceptions

[eigenhombre]

I think this might be a good next ticket before tackling macros. Macros with n-ary bodys will want them, among others.