This tries to add information about when each option was added. It goes
back to version 183.
The version info is included from a separate file to allow generating it,
which would allow more control on the formatting of the final output.
And while we are at it, make 'ssh-authorized-keys' verb properly
documented. Given that OpenSSH documents the interface in its man page
it's fine to just document our implementation of it too.
I started working on a command-line switch to show passwords also in
"pretty" mode. I can submit that code for review if anyone thinks that
woul be useful, but after writing the man page I realized that it's a
fairly niche case, and the hint in the man page is a sufficient
replacement.
