Make app accessible in every request via web['app']

Hi Zed,

I wanted to access to the server's app variable to get stuff I need like the jinja2 environment so I came with this implementation, I don't know if there are better ways to do it as I'm new to python.

This example uses it:
https://github.com/makevoid/fuqit/blob/clean_app/app/index.py#L7

thanks for this mini-framework because by having made it simple, it's fun to hack!