PR57 + Fix

[judgej]

This is PR #57 with a small fix to the position of the "order" element, which MUST come before the [optional] "customer" element. You would not notice this as a problem unless the customer ID is set. The documentation shows no examples with both "customer" and "order" elements in an AIM authorization request, but the test gateway does show up an error if the positions are not correct.

[judgej]

The error we are avoiding is:

{
   "messages":  { 
      "resultCode": "Error",
      "message":  {
         "code": "E00003", 
         "text": "The element 'transactionRequest' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd' has invalid child element 'order' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'. List of possible elements expected: 'billTo, shipTo, customerIP, cardholderAuthentication, retail, employeeId, transactionSettings, userFields' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'." 
      }
   }
}