ARM: software serial port integration (Tx only)

- be careful charging functionality not tested
- work corectly with baud rate 19200 and lover
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- TMR2 is used for Tx timing
- ADC for temp is disabled when Tx soft serial is active (maybe timing problem for other functionality)
- some logic are added for enable/disable some funcionality when eternal temp or Tx serial is active (probably not enough)
I would have left it as it was:
  Serial::flush();
  Serial::end();
this is a standard method to close a serial connection (at least it is used in arduino)
and if you change this, I will need to change also the atmega32 implementation.