[rack-contrib] Rack::Runtime Middleware

[Paul]

I've written some middleware for rack-contrib that add an "X-Runtime"
header with the runtime of the application. Can also set it more than
once, with different suffixes, like this:

use Rack::Runtime, "All"

# use more middlewares here

use Rack::Runtime, "App"

run Application

will set "X-Runtime-All" and "X-Runtime-App" headers on the response.
I sent a pull request to "rack", but I'm not sure who else has commit
rights to the repo.

Here's the branch:
http://github.com/paul/rack-contrib/tree/runtime

Thanks,
Paul