add contribute_to_paddle_cn.md

add chinese doc for gpu-profiling

also, fix another code reference error in en doc.

resolve #834

translation about to chinese by jiangfeng

add chinese doc for gpu-profiling, and fix the out-dated lineNos in en doc referenced to a code file.

resolve #834

fix a index bug

Remove custom glog-like and gflags-like macros

fix a few bugs related to frame size.

Add dependency to gflags and related tests

Add pre-commit hook for contribute documentation.

* Also add a soft link for contribute.md to make github recognize
  this file.

add exclude_patterns for conf.py.in

add Chinese document for demo imagenet_model

Fit pre-commit for clang-format 4.x

Integrate doc en/cn into single doc

Fix enable_virtualenv

The resource "unsigned char[]" array generated by create_source needs to have 0 ending as a valid C string to be used in PythonUtil.cpp initPython()

Change-Id: I5e214606ed9102f37813ea3f07565dc10a9c015e