Add proper command support

[DenuxPlays]

Hey,

I have an idea to properly support commands through clap.
This would enable to write clis or integrate clis into existing applications with proper help output and proper arguments parsing (handled by clap).
Also this would add the ability to autocompletion if we implement it for clap in general.
See here for the current status on auto completion.

I know tasks exist but I think they var/argument handleing is very bad for clis and there is no help output.

Since we already use clap for our own commands the implementation would not be that hard.

Maybe even update the Task trait to support it?

What do you think about that?

[kaplanelad]

It looks good! I'm sure it will improve the CLI experience.
You're more than welcome to open a PR with an example of what you plan to change, and we can discuss it there.

I believe it's important to keep the same interface for consistency.