ATtiny (e.g. Adafruit Trinket, Gemma) I2C library, adapted from BroHogan's code on Arduino Playground: http://playground.arduino.cc/Code/USIi2c
Minor changes for consistency with the Arduino 1.0 Wire library (e.g. uses write() instead of send()). Buffer size slightly increased for Adafruit_LEDBackpack use.
On the Trinket boards, pin #0 is SDA (I2C data), pin #2 is SCK (I2C clock).