Fixed username and currency handling
Added validation to prevent an invalid currency code from being set
Implemented payment_request_id and merchant_notes in line_item
Implemented merchant_notes in subscription_adjustment
Implemented merchant_notes in payment_item
Cleaned up currency fix
Fixed price_ea_cents spelling
Fixed currency handling in payment
Added @XmlElement tag to properly parse currency
Merge pull request #8 from mrostman/master

Fix for currency/username null returns, implementation of various missing fields