add include folder to gitignore
c_library update script: first version

This script can be used with a github webhook to update the
c_library repository whenever the message specifications change
in the mavlink repository.
c_library update script: add example usage
Fix instructions
Fixed rev parse argument
Added URL to origin repo
bail out if nothing changed
Merge pull request #212 from mavlink/clibraryupdatescript

Script to update the c_library repo