Accepted card types

Added a parameter for specifying accepted credit card types.
The get_card_types() method will only return the card_type for
card_types that are in the accepted_card_types variable. The default
is 'all'.
Accepted card types

Added a parameter for specifying accepted credit card types.
The get_card_types() method will only return the card_type for
card_types that are in the accepted_card_types variable. The default
is 'all'.
Improved accepted card types

I made all the improvements that @PawelDecowski suggested in his
comment on my Accepted Card Types pull request
(see https://github.com/PawelDecowski/jQuery-CreditCardValidator/pull/22#commitcomment-2566569).
Merge pull request #22 from gabrieljoelc/master

Option to specify accepted card types