CLI tab-completion

[mads-hartmann]

As all good CLI tools we need to have tab-completion.

• Figure out if we can automatically generate the scripts based on docopt
• Figure out how to ship the completions (brew should have support for this)
• Support zsh and bash.

[mads-hartmann]

This seems like a tool that might be able to generate these completion scripts https://github.com/Infinidat/infi.docopt_completion