introducing per-line alarm register.

 * Added the command 'b' and the relative register to handle a per-line
   alarm enable or disable, with the scope to ignore alarm for certain
   lines.
   This commit will only add the register and the command to set/get it.
   It is not functional yet.
add serial number and fix terminal out.

 * there is now the support for the serial number that
   must be loaded at the first boot after a new firmware is
   uploaded.

 * Serial number can be changed with the command line.
   The change of the serial code shouldn't be exported to the API.

 * terminal out has changed, now reading from input must terminate
   with '\r' char and not with '\n'. This force a major change in
   the API who dialogue with the device.

 * Removed verification of the code from the avrdude programming switch.