Merge ASGIWhiteNoise

[robd003]

Description

I'd really like to get the hard work in this pull request merged in before the next whitenoise release. #359

[robd003]

@evansd Hey Dave, any chance you could put some effort into reviewing this before the end of Jan?

[mlec1]

I am interested in this feature too

[matthiask]

Sorry for plugging my own software, but here's my answer to this:
https://github.com/matthiask/blacknoise

It doesn't integrate with Django and only lives in the ASGI layer. This makes everything to much simpler and seems to work well. It's alpha but I have been running it in production for a few weeks now.

[Archmonger]

For future onlookers, ASGIWhiteNoise has been forked into ServeStatic.