Basically from caffe2::logging.h, but only expose `PADDLE_ENFORCE`
interface.

Change the CpuMatrix::copyFrom and CpuVector::copyFrom with the stream parameter to the synchronous interface.

Make user can check what type is in variable

__must_check is a macro mark of function return value. It let developer
must check the return value is legal or not.

Please use `override` not `virtual` in sub-classes.
`override` can check if there is a method in `parent` while compiling.