api: remove XML code from net_http_adapter

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
api: add first payment and invoice calls

Add ability to charge an account.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
payment_method: revisit plugin_info= method

Support serialization as well as deserialization.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>