`ParseUnverified` doesn't set the token `Signature` field

[slickwilli]

I'm not sure if this was an intentional design choice or just an oversight but ParseUnverified does not currently set the token.Signature field.

Logically, I was expecting this field to still be set even though it is not verified. Extracting it manually is simple enough but I believe ParseUnverified should be functionally equivalent (minus verification).

I have a PR ready to go if this is indeed an oversight.