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

Fix warning

Fix Travis-CI build error.

* error because merge of #711. The old issue don't check pre-commit
  hooks.

Remove m4 when generate protobuf

adding input type check for python data provider

* Also fix a protential bug in WarpCTCLayer.cpp

fix some dead links in doc/

Also fix compile issues

add submodule instructions in build_and_install doc

Add inline and bit manipulation in CpuId.h

Feature/travis pre commit checks

Fix bugs in Docker document

Fix Travis-CI when using rebase.

* The $TRAVIS_COMMIT_RANGE could be not existed, because the git history
  can be changed and rebased. Here we alway run Travis-CI when `git diff`
  cannot return the modified files.
* Also do not push docs update if is not PaddlePaddle/Paddle.