Clap v3 has been released and this PR updates to use it. I did a
cargo upgrade to update all the other dependencies, but if you
prefer me just updraing clap, I can go ahead and do that.
Use assert_cmd for testing cli. This gives a cargo_bin method which
is more convenient for integration tests rather than doing cargo run.
Summary of the updates:
cargo upgradeto update all the other dependencies, but if you prefer me just updraing clap, I can go ahead and do that.