Implement BulkUpload to upload many objects at once - fixes #10

  * BulkUploadResult stores results of Connection.BulkUpload().
  * Connection.BulkUpload() reads data from an input stream and
    sends them to the server.  The server need to support bulk
    operations, or it will return Forbidden error (403).
  * Add reference URLs to comments of Connection.BulkDelete().

See:
http://docs.openstack.org/trunk/openstack-object-storage/admin/content/object-storage-extract-archive.html
http://docs.rackspace.com/files/api/v1/cf-devguide/content/Extract_Archive-d1e2338.html