Update Dockerfile and command name to use "boot2docker-cli"

Also, I've added the main.Version and main.GitSHA here and updated the README appropriately.
Merge pull request #32 from tianon/update-dockerfile-and-command-name

Update Dockerfile and command name to use "boot2docker-cli"
Moved config-related into a separate file
Improved wording of contribution process and code style.
Different message on Windows after starting boot2docker VM

Docker client does not run on Windows for now. People have to SSH into
the VM to work on Windows.
Complain about VBoxManage not found only if necessary
More helpful advice for Windows users
Merge pull request #37 from riobard/refactor/config

Moved config-related into a separate file
Merge pull request #38 from riobard/doc/code-style

Improved wording of contribution process and code style.
Merge branch 'master' into fix/vbm-not-found

Conflicts:
	main.go
Merge pull request #39 from riobard/fix/docker-cli-win

Different message on Windows after starting boot2docker VM
Merge pull request #40 from riobard/fix/vbm-not-found

Complain about VBoxManage not found only if necessary