Add Resilient Packet Ring Interface and Node class.
Tested and it works, but not safe.
Fix issue where messages were accepted at too small length.
Merge branch 'develop' into feature/resilient_packet_ring
Fix inline use in Atmega SPI.
Remove unnecessary header guards from rpr.hpp file.
Merge branch 'develop' into feature/resilient_packet_ring
Merge branch 'feature/resilient_packet_ring' into develop
Merge branch 'develop' into feature/experimental_structure