I'm not sure how far I'm going to take this thing. It's already
functional enough for my purposes. And I'm in the middle of squeezing
the fujinet-chat code down, so this is currently low priority. It
really only exists so I can easily test fujinet-chat against different
FujiNet firmware versions.

However, it could be made more useful, when/if I find the time
and motivation to extend it.

Stuff to do before a 1.0 release:
---------------------------------

- Test with newer esptool versions.

- Test with older platformio versions.

- Find out if it works on MacOS as-is (if not, make it work).
  I think the device nodes aren't /dev/ttyUSB* there... though pio
  should be smart enough to know them, and the -p option should work,
  for users who know what they're doing.

- Config file in ~/.fujinet-updater.conf, to set at least the default
  -t option. Don't actually put this in ~/.fujinet-updater/, since
  the user might want to rm -rf that to clean out old firmwares.

- -d option to delete the ~/.fujinet-updater/ dir afterwards?
  or maybe make this the default, and use -k to keep it? Or
  maybe only delete the downloaded/extracted files, because...

- ...we might log stdout/stderr to ~/.fujinet-updater/log.txt
  or similar.

- -v option for verify? easy to implement (esptool.py has an option
  for it already).

Stuff to do after a 1.0 release:
--------------------------------

GUI frontend. It can be barebones, but it at least should match the
functionality of the official one. Write in C, use GTK (2? 3?).

Alternately, a curses UI. Doubt I'll do both.