Fixed I2C 7-Bit Addressing

The TwoWire Library expects slave addresses to be entered in the
standard 7-Bit format. Added some code to the I2C_Send7bitAddress
function so that the address is bitshift to the left by one, before
performing the bitwise operation to set the R/W bit.
Merge pull request #3 from timothybrown/master

Fixed I2C 7-Bit Addressing