* "remove GPU Sync Interface"

* "fix typo"

* "fix type cast error"

* "fix related Copy with stream"

* "fix failed tests with DevicePool"

* "fix stupid removed position error"

For input argument with a list of variables, drop_empty_grad is not allowed because it makes the correspondence bewteen a variable and its gradient ambiguous. Use REGISTER_OP_EX to register the op or call InputGrad(?,false) in GradOpDescMaker.

* Remove unnecessary reshape in ColwiseSum

Speed up 12s -> 10s.

* Hand write ColwiseAdd in CPU

* Rename XXDescBind --> XXDesc

* Fix Compile

* Updating the design doc of Fluid

* Organizing the operator documentation

* Adding a proposed format for operator documentation

* Adding more details to the format

* Move framework.proto to proto namespace

* Fix compile

* Fix compile

* Fix Compile

* add more place_test and rename Cudnn to CUDNN

* fix ci

* "derived cudnnDevice context"

* "leave remove cudnn handle from CUDADeviceContext"

* "fix math function error"