Fix compilation for gcc5.4

* Support copy in Fluid channels

* Address PR review comments

Enhance LoDResetOp and add python wrapper

Disable the link flags on Mac.

Enable P2P memory copy

On k40 with 4 devices, time reduces from ~4.0 to ~3.8+, should be
more obvious on better hardware

move two images

Limit the symbol table of fluid shared library.

Add distributed lookup table design

Remove unnecessary clone of program in C++ Executor.Run

Add float16 support for pool 2d operator

The error is:

paddle/fluid/operators/math/concat.cc:47:72: error: invalid initialization of non-const reference of type 'paddle::platform::CPUPlace&' from an rvalue of type 'paddle::platform::CPUPlace'
   auto& cpu_place = boost::get<platform::CPUPlace>(context.GetPlace());

Should not use reference for cpu_place.

Add float16 support for cast op

add gserver to capi dep

rm unused private field in profiler

fix regularizer when gradient is None

Update cpp reader doc

delete unused images

Add float16 support for cudnn conv2d