Function signature of .compileAsync()

[RobLoach]

Looking at normalizeFnAsync(), it seems to expect the resulting fn to be a .render() function:

function normalizeFnAsync(result, cb) {
  return Promise.resolve(result).then(function (result) {
    if (result && isPromise(result.fn)) {
      return result.fn.then(function (fn) {
        result.fn = fn;
        return result;
      });
    }
    return result;
  }).then(tr.normalizeFn).nodeify(cb);
}

This is the function that .compileAsync() calls. Since compileAsync expects to result in a render() function, it makes it difficult to work with nunjucks, since the majority of its API is asynchronous. There are other transforms that are affected by this as well.

[RobLoach]

Add Promise support to compileAsync?