Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into Adapting_to_the_BatchNorm_structure_to_support_3D_data

Simplify the CMakeLists for paddle/operator and paddle/pybind

rename sequence into seq to keep a constant style.

add use_mkldnn flag to v2

Update the version of OpenBLAS and fix compiling error caused by std::move on Mac

fix tensor copyfrom bug

Fix clang compiling error of "moving a temporary object prevents copy elision" causing by std::move, and fix some warnings.

Add 3DPoolingLayer

Add Conv3DLayer, DeConv3DLayer

Remove unused including file net/if_arp.h.

don't need to specify the path of libwarpctc.so, refine the python api doc

add a cross_entropy_over_beam layer.

fix download mklml error

fix clang build error