Bump to v3.1.
Bump arduino.mk to stop empty directory from being created.
Add link to CLA.
Add a handler for evented messages with a float value.
Add shared handler for tire pressure.
Automatically flip endianness if neccessary.

This makes the test cases more straightforward.
Add a handler for a seat occupancy sensor.
Make occupancy handler more generic, handle other seats.
Add a "platform" module for platform-level initialization.

Resolved one item from #101.
Explain why control requests are handled in main.cpp.

Resolved anoother in #101.
Update docs on which platforms are supported.

Resolved another in #101.
Note why we aren't using memcpy.

Fixed #101.
Merge branch 'next' into fuelfix