code: function(key, callback) {
        if (key) {
          this.store.proxy.remove(this.prefix + key);
          if (callback) {
            callback(null, key);
          }
        } else {
          if (callback) {
            callback('missing key');
          }
        }
      }
docs: Destroy a stored item
  
  @param {String} key The key of the item
  @param {Function} callback Function called when the operation is done
  @return {callback(err, key)} The callback to execute as result
  @param {String} callback.err Error if occurred
  @param {String} callback.key The key of the destroyed item