Add Boot2docker-CLI and Docker Client for Windows

[tknerr]

Adds Boot2docker-CLI and the Docker client (docker.exe) 1.6.0 to Bills Kitchen.

Context:

• it's the first docker version to officially support windows
• still uses boot2docker in the background, but docker.exe now runs natively on windows
• More on the #docker #windows support here: http://azure.microsoft.com/blog/2015/04/16/docker-client-for-windows-is-now-available

Usage:

• before you can run the docker commands, run b2d-start to start the boot2docker VM and set the env vars for docker client
• now you can run docker ps, docker images, etc..
• the boot2docker VM usually keeps running in the background, but you can always stop it via b2d-stop