Support Quoting of Dotted Pairs

[iwillspeak]

Currently dotted pairs are quoted as a list conianing the dot as an identifier. It
seems like Scheme expectes them to be quoted as a pair instead. It could be
that we need to add support for pairs as a new literal type too.

Given:

'(a . b)

We expect it to become:

(a . b) ; ~> (pair (quote a) (quote b))

But in fact it becomes:

(a |.| b) ; ~> (list (quote a) (quote |.|) (quote b))

[iwillspeak]

Part of this comes down to the fact we should just support improper tails as parts of forms. The parsed form also needs modifying before we bind it. Maybe a separate CST and AST is the way forward here. CST could capture the raw representation of a given form, but the AST always represents it as Form(List, Option) where the second node is the improper tail.

Something like Rowan's red-green trees here might be the way forward.

[iwillspeak]

Fixed by #55:

§> '(1 . 2)
}= (1 . 2)
§> '(1 . (2 . 3)) 
}= (1 2 . 3)
§> '(1 . (2 . '()))
}= (1 2 quote '())
§> '(1 . (2 . ())) 
}= (1 2)