This is mostly intended to be invoked from cryptsuite, so that I can
make test certificates with various features to check the validation
function. But it also has a command-line interface, which currently
contains just enough features that I was able to generate a
certificate and actually make sure OpenSSH accepted it (proving that I
got the format right in this script).
You _could_ expand this script into a full production CA, with a
couple more command-line options, if you didn't mind the slightly
awkward requirement that in command-line mode it insists on doing its
signing via an SSH agent. But for the moment it's only intended for
test purposes.
