implemented the customer resource #79
took out sleep, removed positional args for credit and debit
abstracted out adding an item to a customer
changed customer to be created through marketplace, refactored add_item to extract_uri_from_object, refactored active_bank_account and active_card
added support for adding an untokenized card to a customer
modified transaction spec to load object first and then test
removed transaction spec
fixed on_behalf_of attribute setter for customer
Merge pull request #82 from rloomba/customer

implemented the customer resource #79