The sleekxmpp.xmlstream.tostring and sleekxmpp.xmlstream.tostring26 packages
have been merged to sleekxmpp.xmlstream.tostring. The __init__.py file will
import the appropriate tostring function depending on the Python version.
The setup.py file has been updated with the package changes.
ElementBase is now a direct descendent of object and does not subclass ToString.
Stanza objects now return their XML contents for __repr__.
