Adopt a CLI specific library

[willianpaixao]

At the moment the arguments are read and parsed using os.Args. This approach leaves little room for improvement of the CLI tools.

I suggest the adoption of a specialized library, like github.com/spf13/cobra or github.com/urfave/cli. A huge number of improvements would be possible out of the box.

Please refer to their documentation for an extensive list of features.

[bitgamma]

while it surely would have made sense to develop the app using one of these libs, adopting it now is quite a task. That said, a PR would be absolutely welcome!