code: function loadSingle(source) {
    var promise;
  
    if (source.match(/^https?:\/\//)) {
      promise = httpGetPromise(source);
    } else {
      promise = readFilePromise(normalizePath(source));
    }
  
    return promise;
  }
docs: Loads a single static asset from either a filename or URL
  
  @param {string} source The source document to load
  @return {Promise.<string>} The file contents