- categorize diagnostics as fatal or warning. done in the code, needs doing
  in the man page.

- fix dup message for bad opts:
  $ ./unalf -X
  ./unalf: invalid option -- 'X'
  unalf: fatal: invalid option (try -h or --help)

- include some of Alfred's email commentary in the doc dir.

- create some alf archives and hexedit them to introduce errors, make
  sure unalf doesn't segfault or get stuck in a loop (it should
  *always* exit cleanly).

- reverse-engineer the LZ.COM binary, so we have a compressor.
  this would be more of "just to say I did it" thing, there's no real
  need for it. alternatively, see if I can rewrite the compressor
  in C.