more documentation
fix issue where JSON output would be malformed due to sourcekitten crashing
Merge branch 'master' into jp-objc

* master:
  fix issue where JSON output would be malformed due to sourcekitten crashing
- refactored to remove unnecessary var's that could be let's
- combined compiler extraction functions into compiler_arguments_from_xcodebuild_output(_:language:)
move all compiler argument filtering into compiler_arguments_from_xcodebuild_output(_:language:)