Support Shell and CLI modes

[lidel]

Eg:

• https://github.com/spf13/cobra (overkill)
• https://github.com/codegangsta/cli
• https://github.com/mkideal/cli (simple, best docs with examples so far)

[lidel]

These days we will probably go with cli+shell approach:

• https://github.com/desertbit/grumble