code: function save(callback) {
      var info = {
        version: pkg.version,
        key: key,
        modules: {},
        emitModules: {}
      };
  
      _.each(modules, function(module, src) {
        info.modules[src] = _.pick(
          module,
          ['src', 'srcHash', 'dest', 'destHash', 'dependencies', 'emitModules', 'emitFiles', 'cached', 'url', 'extra']
        );
      });
  
      _.each(emitModules, function(module, src) {
        info.emitModules[src] = _.pick(module, ['src', 'emitCached']);
      });
  
      fs.writeFile(path.resolve(directory, 'miaow.cache.json'), JSON.stringify(info, null, '  '), callback);
    }
docs: 保存缓存日志