Adding a cli library

[MariusVanDerWijden]

Would you be open to move the cli/flags handling from the basic-builtin handling to some library?

[ralexstokes]

I'd support this, esp for the right library -- is there one you have in mind?

I assume the intent is to simplify or harden the current flags infrastructure?

[MariusVanDerWijden]

Yes exactly, I would use https://github.com/urfave/cli which is the one we use in go-ethereum.
Theres a lot of dereferencing of flags going on which feels a bit unsafe