Feature: Support Rack apps mounted within other Rack apps

[ghost]

Hi, please consider the situation when you are building Sinatra based app which will be later mounted on some sub-uri, the usual case "/admin". The requests for necessary files will end up in totaly wrong rack app. I think this could be easily solved by analyzing request.script_name as Sinatra does.

[pboling]

Great idea! I had not considered running it in a mounted rack app.