Fix an embarassing bug where another SCL clock cycle was initiated after the last byte is read.
Also fixed up slave NACK. SLA_NACK will now cause the xfer to stop, and the actual byte count read is now sent to the host.
ref: https://github.com/ginge/OpenServo/issues/1
Updated usbtiny to version 1.7
Tided some code formatting  up and indents