remove requirement file
refactor code for PaymentSystem#parse_transactions and PaymentSystem#parse_accounts so that it's easier to follow
add extra commands to ensure that the code does not let accountholder's balance go over limit
fix the code so that it will never let accountholders go above their limits, also included a bunch of debugging puts statements
remove debugging puts statements and refactor Person#transact
reverse the sign for credit and charge, I got it mixed up earlier
add validation to ensure that cards with greater than 19 digits are invalid, commands.csv updated to include such an example
add readme file