Performance tweaks to address #9

- added delays to stop/start listening on RPi
- removed buffer flushes on start/stop listening for RPi
- added modified transfernbd function to BCM library - one has no
delays, also removed one delay period from both by waiting for RX data
- modified transfernb function to stop sending if RX fifo is full
- added delay to stoplistening for arduino etc. (actually seems to
improve performance)
- tests on-par with Arduino performance