constructor(username, auth, apiBase) {
      super(auth, apiBase);
      this.__user = username;
   }
Create a User.
@param {string} [username] - the user to use for user-scoped queries
@param {Requestable.auth} [auth] - information required to authenticate to Github
@param {string} [apiBase=https://api.github.com] - the base Github API URL