add credit card format example

[hartzis]

Love the simple focus and straightforwardness of this library!

Thoughts on adding a credit card format example in format.js?

Found some code from cleave.js for formatting for credit cards as a reference.
https://github.com/nosir/cleave.js/blob/master/src/shortcuts/CreditCardDetector.js

[istarkov]

I think to create standalone library with different universal formatters, possibly will add there I think.