split out cmd functionality

[willscott]

we have a lot of unrelated things going on in the cmd package here.

We should ideally split out:

• full standalone / production-mode operation (e.g. mirror) into it's own command that uses this engine library.
• Utilities we expect providers to run (like verify) into a tools CLI DONE in ipni-cli
• A simple reference provider of car files that other providers can refer to in order to quickly see how to integrate the engine library.

[masih]

As in separate provider mirror into mirror executable? If so, I am curious why?

[willscott]

• reduces surface area of the code in the binary that's deployed / running on the internet
• reduces dependencies / complexity of the download of tools needed for providers running things like verify
• makes it clear what the reference code path is for people looking at it

[masih]

Are you thinking we have an executable for each of those? From usability perspective I am not sure it makes sense to do a go install for each. Re dependencies, How much does it matter when the executable itself is small anyway?

Having said all of this, happy to discuss the restructuring further over a PR; that would help me get my head around the changes.