Added I2C Support

Added I2C support. This should obviously be peer reviewed. I tested using an 8x8 Matrix LED display. Results are identical for Arduino and BBB. I also threw together a quick demo for the TMP102 temperature module, and results are identical for Arduino and BBB. 

I am not sure if it worth providing tests for the 3 i2c methods, since there is no pin manipulation to test.
Not sure what you thoughts on this might be.