add local recordio reader interface

[gongweibao]

fix #2542

[helinwang]

CI failed because:

04:39:55]	[Step 1/1] File "/paddle/python/paddle/v2/reader/tests/.test_env/local/lib/python2.7/site-packages/paddle/v2/reader/creator.py", line 68, in reader
[04:39:55]	[Step 1/1] f = recordio.reader(path)
[04:39:55]	[Step 1/1] NameError: global name 'recordio' is not defined

Probably need to add pip install RecordIO package into the build process.

[helinwang]

We are following PEP 8 naming convention, please see: https://stackoverflow.com/a/159745/852385

[gongweibao]

我看到文档设计的是大写，所以。。
我改过来。Done

[helinwang]

不好意思！写文档的时候没注意。

[helinwang]

Great! Just a reminder that we will use paddle.v2.reader.creator.RecordIO for both local and cloud training (do not need to do in this PR).
Our goal is to reuse the same reader for local or cloud training:

PaddlePaddle提供专用的data reader creator，生成给定RecordIO文件对应的data reader。无论在本地还是在云端，reader的使用方式都是一致的

The training in cloud the trainers will talk with the master server, so need to integrate with this PR: #2551

[helinwang]

LGTM++ after the naming convention is fixed.

[typhoonzero]

Need to add python dependency "recordio" to make the CI pass