Please add batch.GetTokenAccountBalance

[JavinYang]

GetTokenAccountBalance is available in the rpc client but not in the batch. I urgently need this function.

        public void GetTokenAccountBalance(string pubKey, Commitment commitment = Commitment.Finalized,
                               Action<ResponseValue<TokenBalance>, Exception> callback = null)
        {
            var parameters = Parameters.Create(pubKey, ConfigObject.Create(HandleCommitment(commitment)));
            _composer.AddRequest("getTokenAccountBalance", parameters, callback);
        }