Splits up project into smaller files.

- Moved configuration and global constants into thermo_config.h

- Changed some int types to byte to squeeze in a byte here and there.

- Changed display_err() to display_msg() so we can use this for
  reporting status changes.  Also added bootup messages so we
  get some feedback on what is going on.

- Changed serial output a bit for the values so they are easier to cut
  and paste into files to plot data.  (Not really useful, but we'll
  get back to that)