Fix incorrect description of MNStorage.create() object parameter
For the API documentation at:
We describe the object bytes transmittal with
Transmitted as an UTF-8 encoded XML structure for the respective type as defined in the DataONE types schema, as a File part of the MIME multipart/mixed message.
This would be correct for, say, the sysmeta parameter, but the object bytes are an encoded blob. Check the other API calls with the 'object' parameter to make sure they're correct too.