mb2hal: now using libmodbus3, added improvements.

- Mb2hal now uses libmodbus3 instead of the old libmodbus file
  located in src/hal/user_comps/modbus.c used by gs2_vfd.c
  # Also fix a TIMEOUT bug (due to this unpatched old libmodbus file).
- Better INI file documentation (HOW-TO).
- Better Submakefile.
- Source code cleaned and reordered.
  # Now is posible to add new functionallity.

See LogBook.txt for more information.

Signed-off-by: Michael Haberler <git@mah.priv.at>