Larger messages seem to reduce range dramatically, presumably
because a larger message increases the chance for flipped
bits or errors. To combat this, I'm introducing multiple message
types, sending only the data necessary for the specific message
type. Previously we were sending one giant message with a superset
of data.

To do this, we need a header, which is 8 bits:

MSB  00000000  LSB
     RRRAAAMM

MM - message type
     00 - contains sensor data message
     01 - pairing, contains keys message
     10 - reserved
     11 - reserved

AAA - sensor address (if applicable to message type)

RRR - reserved (could be message-specific info)

Messages will consist of a 1-byte header, and a 16 byte payload.
There is currently a 'sensordata' payload, and a 'pairingdata'
payload.
sensor-listener: first draft at supporting new message format
sensor-listener: fix mask of header, print message type for debugging
sensor-listener: do not rely on fixed buffer size and assume sql will fit, fix segfault when no config passed
sensor-listener: fix signature verification for new message types