constructor(auth, apiBase, AcceptHeader) {
      this.__apiBase = apiBase || 'https://api.github.com';
      this.__auth = {
         token: auth.token,
         username: auth.username,
         password: auth.password,
      };
      this.__AcceptHeader = AcceptHeader || 'v3';

      if (auth.token) {
         this.__authorizationHeader = 'token ' + auth.token;
      } else if (auth.username && auth.password) {
         this.__authorizationHeader = 'Basic ' + Base64.encode(auth.username + ':' + auth.password);
      }
   }
Initialize the http internals.
@param {Requestable.auth} [auth] - the credentials to authenticate to Github. If auth is
                                 not provided request will be made unauthenticated
@param {string} [apiBase=https://api.github.com] - the base Github API URL
@param {string} [AcceptHeader=v3] - the accept header for the requests