improved xbee_conPurge()
fixed xbee_frameWait()
fixed libxbee::Con::Tx() - now throws a libxbee::xbee_etx
xbee_conRx() can now be called to just get the number of packets in the buffer
added C++ compatibility with byte vectors
added noWaitForAck flag so that xbee_conTx() will return straight away
added xbee_conxTx() and friends to allow tracking of frame IDs
moved eofCallback prototype into a typedef
added a simple_at that doesn't use callbacks