Add Payment provider

Add `Faker\Provider\Payment`:

    creditCardType         // 'MasterCard'
    creditCardNumber($type = null) // '4485480221084675'
    creditCardExpirationDate($valid = true) // DateTime('2014-10-23 13:46:23')
    creditCardExpirationDateString($valid = true) // '10/14'

Supersedes PR #157