Add a passthrough attr to CanBus to allow explicit control.

See #222.
Wrap lines at 80 chars.
Update to latest message format with refactored control commands.
Add a control command to enable/disable passthrough of each CAN bus.

See #222.
Merge branch 'next' into 222-passthrough-cmd

Conflicts:
	src/can/canutil.h
	src/tests/command_tests.cpp
Fix and test serializing passthrough command responses.
Fix a broken test that was lost in a merge conflict.
Log a message when changing bus' passthrough status.
Fix a misleading log message during CAN init.
Switch back to 'next' branch of Python lib, changes are merged.