Commited first version of schematic and PCB design.
Please note, that this version uses ATmega88 uC, running
at 3.3V Vcc and 12.288 MHz clock.
The ATmega88 uC is used as:
1. Clock source for CS5343/4
2. Interface to switches
3. Interface to potentiometers

State of switches and potentiometers is reported do RPi via
I2C interface (ATmega is I2C slave).
ATmega may be programmed from the RPi using the avrdude program,
as described in
http://kevincuzner.com/2013/05/27/raspberry-pi-as-an-avr-programmer/