Update all the debian and ubuntu images with the newer debootstrap script

This includes running "apt-get update" as the last step of each image, and fixes some problems that were specific to the ubuntu:lucid image.

Finally, I've added more debian images:
- debian:stable, debian:testing, debian:unstable are all tagged to the "release" in /etc/apt/sources.list
- debian:experimental and debian:rc-buggy include the "experimental" repository on top of sid/unstable
Add CirrOS Docker Image

"CirrOS is a Tiny OS that specializes in running on a cloud."

This stackbrew image is maintained by Eric Windisch,
while CirrOS itself is maintained by Scott Moser.

More on CirrOS may be found on its launchpad page:
    https://launchpad.net/cirros
Merge pull request #24 from tianon/update-debian-and-ubuntu

Update all the debian and ubuntu images with the newer debootstrap script
Merge pull request #27 from therealprologic/master

Added Official CRUX Linux (http://crux.nu) Docker Image
Merge pull request #26 from ewindisch/master

Add CirrOS Docker Image
Update README with more up-to-date information about how to contribute (ie, not updating MAINTAINERS and instead using a `# maintainer: ...` comment)
Merge pull request #29 from tianon/update-readme

Update README with more up-to-date information about how to contribute
Update docker-dev for v0.8.0
Merge pull request #30 from tianon/update-docker

Update docker-dev for v0.8.0
Added tag 3.0 for current CRUX release