Paddle need requests package to download file.
Fixed #1956

update design doc: add how to convert dataset and use converted dataset

fixed error in beam_search example and documents

Fix protobuf.cmake to handle empty PROTOBUF_VERSION correctly

Sometime FIND_PACKAGE(ProtoBuf) get an empty PROTOBUF_VERSION. In this case, ${PROTOBUF_VERSION} needs to be quoted.

Try to remove ParallelParameter.

It seems that is not used.

Change PROJ_ROOT in CMakeList.txt to use CMAKE_CURRENT_SOURCE_DIR

fix typo in git usage

Disable some unit tests when PYTHON or SWIG_PY are not enabled.

update git usage doc

* When SWIG_PY is not enabled, paddle.v2 package cannot be used.
* When PYTHON is not enabled, PyDataProvider cannot be used.

Fix issue #1920

Skip cpplint if source is not changed.

Change-Id: Ia29cd3d205e401dc3d04fbaf3cba2b01f2f4f0ca

Update author list

make docker build command for building prodction image more precise

complete the doc that guides generating paddle docs

Update docker readme to reflect changes.

refine the level of title in k8s_basis_cn.md

Smoothl1 loss and Python API.