Add tokenizers module

Author: gpengzhi

texar/tf/data/__init__.py

@@ -15,4 +15,5 @@
 Modules of Texar library data.
 """
 
+from texar.tf.data.tokenizers import *
 from texar.tf.data.data_utils import *

texar/tf/data/tokenizers/__init__.py

@@ -0,0 +1,19 @@
+# Copyright 2019 The Texar Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Tokenizer modules of Texar library.
+"""
+
+from texar.tf.data.tokenizers.bert_tokenizer import *
+from texar.tf.data.tokenizers.tokenizer_base import *