* add numpy bridge

* fix template compile

* add unittest, add default
test=develop

* fix unittest
test=develop

* fix unittest
test=develop

* zero_copy=True for to_variable,
test=develop

* bug fix
test=develop

* disable deprecated NumPy API
test=develop

* use better design of NumpyAllocator
test=develop

* fix Py_None check
test=develop

* reset c++ tracer when jump out dygraph guard
test=develop

* refine PADDLE_ENFORCE_xx format
test=develop

* bug fix of tracer switch
test=develop

* update decref
test=develop