Add early draft of imdb.py and unit test

python/paddle/v2/dataset/imdb.py

+# /usr/bin/env python
+# -*- coding:utf-8 -*-
+
+# Copyright (c) 2016 PaddlePaddle 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.
+"""
+IMDB dataset: http://ai.stanford.edu/%7Eamaas/data/sentiment/aclImdb_v1.tar.gz
+"""

python/paddle/v2/dataset/tests/imdb_test.py

+import paddle.v2.dataset.common
+
+URL = 'http://ai.stanford.edu/%7Eamaas/data/sentiment/aclImdb_v1.tar.gz'
+MD5 = '7c2ac02c03563afcf9b574c7e56c153a'
+
+paddle.v2.dataset.common.download