Preallocated buffers with various preambles etc. Used SPI_TransferBlock for
anything over a few bytes instead of burstWrite. Also make more of the
communications wrappered in a large semaphore grab using a new rfm22_write_noclaim()
Still needs work - probably because most of the methods to repeated calls they should
all use the noclaim, or more specifically that function becomes rfm22_write/read.