Updated PaymentStatements table.
Added CreditHistory member variable.
Added methods for dealing with each balance bin individually.
Updated applyPayment to reflect the availability of a PaymentStatement,
and to only apply fees and interest up to the value specified in the
PaymentStatement, rather than the whole loan. Added escape if the
PaymentStatement pays off the whole loan and a refund if it is too much.
Automatically applies negative fee and interest balance from previous
payments to the current payment. Now makes an attempt to call the proper
credit history records.
Added new fields into SendOutStatement entires in the PaymentStatements
table.
Updated CreditHistory table.
Added toString() method.
Added method to get the type of the CreditEvent.
Implemented recordPayment method