* PyBind and SWIG of paddle cannot be load in a single Python process,
  lazy import all SWIG library of Paddle. Otherwise, the glog, gflags
  are imported twice in a same Python process.
* Note that all PyBind11 return C++ std::string as an unicode. For
  protobuf, it is need be cast to `str` before use them.
* Add unit test for Get `OpProtos`

* Also fix some other bugs.
* Fix #1495

remove inferencer and Inference from __All__, since infer is sufficent, they are implementation detail.

rename inferencer.py to inference.py