Use non-blocking I2C library for improved performance

Trying to add I2C devices to current stepper firmware (encoder, temp sensor), but I'm noticing the controller will lock up when one of the devices doesn't communicate. This is due to the use of the Wire library, and specifically the blocking while (Wire.available() == 0) infinite loop.

Perhaps using a non-blocking i2C library (such as nI2C) would help? I think this might also help with #19 and overall motion performance.