Test
----
rspec ./card_processor_spec.rb

Here are some sample commands and responses.
"./card_processor.rb Add Quincy 1234567890123456 2000"
"Quincy: error"
"=--=-==--==-"
"./card_processor.rb Add Tom 4111111111111111 1000"
"Tom: 0"
"=--=-==--==-"
"./card_processor.rb Add Lisa 5454545454545454 3000"
"Lisa: 0"
"=--=-==--==-"
"./card_processor.rb Charge Tom 500"
"Tom: 500"
"=--=-==--==-"
"./card_processor.rb Charge Tom 800"
"Tom: declined"
"=--=-==--==-"
"./card_processor.rb Charge Lisa 7"
"Lisa: 7"
"=--=-==--==-"
"./card_processor.rb Charge Quincy 200"
"Quincy: error"
"=--=-==--==-"
"./card_processor.rb Credit Lisa 100"
"Lisa: -93"
"=--=-==--==-"
"./card_processor.rb Credit Quincy 200"
"Quincy: error"