Error when no valid certs are found when verifying instead of accessing oob.
Warn when CSRs are found instead of silently ignoring them.
Co-authored-by: Mat Byczkowski <mbyczkowski@gmail.com>
This splits the logic into a cli, which handles parsing command line args and
reading files, and a terminal abstraction for handling user input and ouput.
All uses of os.Exit are removed in favor of returning errors.
Overall this enables better testing and reuse of code. Previously we had to
rely on external unit testing for CLI tests, which are harder to write tests.
