Stable Release of Hack Clock v2.0

This is the stable release Hack Clock v2!

Installation instructions available at https://github.com/deckerego/hack-clock/blob/master/README.md

Coding lessons are available at http://hackclock.deckerego.net/lessons/

The hardware and software now fully supports:

• I2C audio
• Raspberry Pi Zero support
• Programming by block (using Blockly)
• Multiple simultaneous buttons (input pins)
• Support for switches (output pins)
• Debian packaging for ease of installation