Added fingerprint field to Card constructor, bumped to 0.8.0

The API has a "fingerprint" field inside a Card object that uniquely identifies a card. This allows consumers of the API to deny credit cards based on the fingerprint, while maintaining PCI compliance. No reason not to have it. I'm going to use it to patch a hole in the referral system I'm building.

From the docs.


> You can use the fingerprint parameter that's available on a charge object's nested card or a customer object's active_card to uniquely identify a card in your account. If you've decided that you'd like to block a certain card, you  can safely detect it based on the fingerprint.[/quote]
> https://support.stripe.com/questions/blocking-certain-card-numbers
```haskell 
Card  { cardType = "Visa", 
           ,cardCountry = Just "US"
           ,cardLastFour = "4242"
           ,cardExpMonth = 9
           , cardExpYear = 2014
           ,cardFingerprint = "vVbWfR9fR23vbUPw" -- works for me
           ,cardChecks = CardChecks {
                              checkCVC = Passed
                              , checkAddrLineOne = Passed
                              , checkZip = Passed
                              }
          }
```