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

install ccache in Dockerfile to speed up compile

Fix shfl_sync for CUDA8.0

Add float16 support to save op

Change `customize_loss_grad` to `use_default_grad_scale`.

Fluid new API scaffolding

* Fix CPPLint issues in lstm_cpu_kernel.h

* Fix CPPLint issues in math/math_function_test

* Fix CPPLint issues in math/math_function_test

* Fix CPPLint issues in math/concat.cc

* Fix CPPLint issues in math/concat.cc

* Fix CPPLint issues in math/concat.cc

* Fix CPPLint issues in math/gru_cpu_kernel

* Fix CPPLint issues in math/selected_rows_functor_test.cu

* Fix compile error

* Fix compile error

* Build: simplify travis CI script.

* Add linkcheck and run gen_doc in host machine not in docker.

* Add LinkCheck python package.

Update Intel AUTHORS.md

fix build: cuda_helper.h not found

* "re-commit "

* "picked up"

* "fix ci"

* "fix pdb hang up issue in cuda 9"

* "fix cuda9 error"

* "change commit id"

* "remote git tag"

Add FLAGS_cudnn_algo_use_autotune

Added kernel to Beam Search OP

Update AUTHORS.md