docs: function defaultMigrationLoader(dir) {
      let list = new List;
      
      return new Promise((resolve, reject) => {
          fs.readdir(dir, function(err, files) {
              if (err) return reject(err);
              
              const migrationFiles = files.filter((file) => file.match(/^\d+.*\.js$/)).sort();
              
              migrationFiles.forEach((file) => {
                  let mod;
                  try {
                      mod = require(path.join(dir, file));
                  }
                  catch (err) {
                      return reject(err);
                  }
                  
                  list = list.addMigration(file, mod.up, mod.down);
              });
              
              resolve(list);
          });
      });
  }