def find_file_refs_by_extname(extname)
      project.files.select do |file_ref|
        File.extname(file_ref.path) == extname \
        && is_file_ref_included_in_application_target?(file_ref)
      end
    end
def find_file_refs_by_extname(extname)
      project.files.select do |file_ref|
        File.extname(file_ref.path) == extname \
        && is_file_ref_included_in_application_target?(file_ref)
      end
    end
Discover all references to files with a specific extension in project,
 which belong to a resources build phase of an application target.

 @param  [String] extname
         the extname, which contains a leading dot
         e.g.: '.bundle', '.strings'

 @return [Array<PBXFileReference>]