Removed uncommented reference to unused c files.
Added a build info macro in the makefile

This can be used for printing the build info on each node at run time.
Added missing documentation for gps_get_fix

Also added missing const specifier in checksum prototype.
Explicitly enabling can interrupts in GPSNode
Fixed indentation in can.h
Renamed the old DIGITAL_TOGGLE to DIGITAL_INVERT
Merge branch 'master' of https://github.com/UnicornRaceEngineering/g5-nodes
Added more consistent comments in can.h
Cleaned up comments in can.c
Merge branch 'master' into issue2