Improve the way we handle the various parsing "states". Until now

Improve the way we handle the various parsing "states".  Until now
we've hard-coded the state transitions in the command definition file,
but that's error-prone and, worse, it's redundant--we can figure out
what state we're in anyhow.  We can cleanly handle INPUT PROGRAM and
FILE TYPE with a nested command-processing loop.

Improve command name completion for readline.