code: function lineToTodoMapper (filename, sha, conf) {
    return function lineToTodo (line) {
      return _.merge({
        "file":   filename,
        "sha":    sha,
        "line":   line.ln
      }, extractTodoTitle(line.content, conf));
    };
  }
docs: String, Sha → String → {file, sha, line, title, label}