Modernize app engine demo: py27, non-CGI interface, get_template_namespace.
Remove markdown support from app engine blog demo.
Use autoescape in appengine blog demo.
Remove embedded copy of markdown.py from blog demo.
Use autoescape in blog demo.
Use distinct cookie names across all the demo apps.
Autoescaping is now the default, so remove the explicit setting in chatdemo.
Use autoescape in websocket chat demo.