Support for Bulk Upload.

* 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().

References:
* [OpenStack admin guide](http://docs.openstack.org/trunk/openstack-object-storage/admin/content/object-storage-extract-archive.html)
* [Rackspace API](http://docs.rackspace.com/files/api/v1/cf-devguide/content/Extract_Archive-d1e2338.html)

See #8 for discussions, #9 for bulk delete.