message: generate_docs.sh: return 1 if warnings are found
  We should trigger a CI fail if docs are missing.
diff: @@ -32,9 +32,20 @@ fi
  # Build and install locally.
  make INSTALL_PREFIX=$install_prefix default install
  +return_result=0
  # Doxygen likes to run where the source is (because INPUT in .doxygen is empty),
  # so we cd there.
  pushd $install_prefix/include/dronecore
  -doxygen $source_dir/.doxygen
  +# If any warnings are thrown, we should not flag this as a success.
  +doxygen_output_file=".doxygen_output.tmp"
  +doxygen $source_dir/.doxygen &> $doxygen_output_file
  +cat $doxygen_output_file
  +if cat $doxygen_output_file | grep warning
  +then
  + return_result=1
  + echo "Please check doxygen warnings."
  +fi
  $source_dir/generate_markdown_from_doxygen_xml.py $install_prefix/docs $install_prefix/docs
  popd
  +
  +exit $return_result
  