Configure or override payment service settings.

Use the configuration object to set/override required service settings.
Alternatively you can use the default settings.

List of settings
----------------
mode - set the service mode mode. Allowed values: :sandbox, :production
(use the :production setting for live environments, sandbox otherwise).
Default: sandbox

api_version - set the api version to use. Default: "2013-01-01"

region - set the region which defines the right enpoint to use. Allowed
values: :eu, :us. Default: :us

seller_id - The seller or merchant identifier that you received when
you registered for Amazon MWS. No default. Required.

access_key - The AWSAccessKeyId that you received when you registered
for Amazon MWS. No default. Required.

secret - Used to generated the request signature. Your Secret Key is a
secret that only you and Amazon should know. It is important to keep it
confidential to protect your account

(See
http://docs.developer.amazonservices.com/en_DE/dev_guide/DG_Registering.
html,
http://docs.developer.amazonservices.com/en_DE/dev_guide/DG_RequiredRequ
estParameters.html,
http://docs.developer.amazonservices.com/en_DE/dev_guide/DG_ClientLibrar
ies.html#DG_OwnClientLibrary__Signatures for more information about
seller_id, access_key and secret)
Amazon OffPayments API Client

The PaymentService is a wrapper around the Amazon OffPayments API. See
http://docs.developer.amazonservices.com/en_DE/off_amazon_payments/OffAm
azonPayments_Overview.html for details about the API.
Add amazon payments usage example
Merge pull request #2 from mwallasch/amazon-payments

Setup amazon payments api client