Refactor CLI code to use Cobra

[kehoecj]

This was proposed by the community a while ago but it seems like a good time to refactor our CLI logic from using Flags to COBRA. Cobra offers a lot of functionality such as setting values from environment variables instead of/in addition to command line args, autocompletion, auto generated man pages, etc

[1garo]

I would like to contribute to this issue!

[kehoecj]

I would like to contribute to this issue!

@1garo It's yours!

[1garo]

@kehoecj working on it!

While reading the readme I came across the build part, have you ever thought about creating a Makefile? I could do it.

Maybe something like:

$ make mac
$ make mac-install

$ make win
$ make win-install

$ make linux
$ make linux-install