Revision 3

- implement calibrate temperature sensors using two 16 bits values (multiplier+offset)
- changed watchdog handling to prevent possible crash
- layout of the eeprom address space using virtual struct
Change clock to PLL clock (16 Mhz) to give I2C
a little more space.
Cosmetics
Use watchdog for what it's for, reset after 8 seconds of hang.
Watchdog timer interrupt served by timer0 now.
Revision 4
Throttle PLL CPU clock when writing to or reading from EEPROM,
the EEPROM can't handle a PLL CPU clock of higher than 8 Mhz.
Revision 5.