Initial commit for SBP message header generation code.
Add DOPs message definition.
Fix sbp_decode undefined references.
Add message type number definition in python file.
Rename python to sbp_messages.py to match C header.
Update header guards to avoid conflict.
Ignore some junk
Merge branch 'sbp_messages'

Initial standard SBP message definitions and scripts to generate Latex, C and Python from a YAML file.