I don't really understand why we were using `linefeed::Reader`
directly, but reading is not the full set of linefeed features we want
to access. I think the `linefeed::Interface` should be owned by the
`Repl`, not the `InputReader`, but it's a little awkward to share
access with that configuration, so I'm not going to lift the ownership
until I have a reason to.
I think the "--no-tty" argument might be useful for running inside
Emacs. Along the way, I made read_stdin() strip the trailing newline,
which agrees with InputReader::read_line().
c19337c8bf