Get the core Credit Memo mappings based on docs at
https://developer.intuit.com/docs/95_deprecated/qbd_v2/qbd_v2_reference/0600_object_reference/creditmemo
Ensure that a line item is initialized
Associate Detail with Windows module PaymentDetail
Add in credit memo requires
Edit some of the fixure data
Add in credit memo service and spec
Add Credit Memo to the README's supported services table
Merge pull request #123 from minimul/credit-memo

Credit memo support.