some cleaning
making progress on 'existing buyer makes a purchase with an existing card.

Yet another #469 victim.
Making progress on 'new buyer makes a purchase'

Another #469.
Progress on existing buyer makes a purchase with a new card.

Closes #476.
Add credit card scenarios.
making progress on 'adding a card to a customer'
New feature: AVS postal code matches
New feature: AVS postal code does not match
New scenario: AVS Postal card is unsupported
Making progress on 'AVS postal code is unused.

#438 will fix this.
New feature: AVS street matches
New feature: AVS street does not match
Making progress on 'avs street match is null'

#438 will fix that.
Progress on 'detect a visa card brand'

#438 fixes
Make progress on 'detect a mastercard brand'

#438 fixes
Make progress on 'detect an amex brand'

#438 fixes
make progress on 'detect a discover card'
Make some progress on retrieving card info

#480 is tracking this.
Progress on 'tokenizing a card'

#438 is the problem.
Making progress on luhn test failure