Add option to print results as xcode warnings for build phases

[voidless]

Add support for usage in Xcode build phases. Xcode uses the following format for log warnigs: path/to.file: severity: error message

Usage:

path/to/fengniao --project . --xcode-warnings

Don't fail build phase with warnings:

path/to/fengniao --project . --xcode-warnings || true