radio rx/tx performance improvements.
big improvements to radio layer. fixed a bunch of little race conditions that stick out when sending data really fast.
cleaned up radio.c a little bit, updated README
added code to handle tx underrun and rx overflow.
fixed up the tx underflow protection code. the radio engine looks pretty bullet proof now.
cleaning up radio and adding clear bool func
added sample capture of tx/rx data
initial structure of the csma layer designed.
preliminary implementation of csma.