+ added powerDownCode
(code/interface is experimental, test + refactor needed)
+ added RDY test in several places
+ removed smooth2Value() => sample sketch
+ extended test sketch
+ tested on 100, 400, 800 KHz (works)
+ added readEEPROM
+ added RDY (to check EEPROM write is done)
+ writeDAC() has got a flag for writing to EEPROM
+ prepare for PowerDownMode
+ cleaned up code a bit (some more still needed)