* support setup.py to compile custom op

* move file into paddle.utils.cpp_extension

* support python setup.py install

* refine code style

* Enrich code and add unittest

* Polish code and api doc

* fix cpp_extension not include in package

* fix relative import

* fix os.makedirs exist_ok param compatibility PY2

* add compile flags in test_jit_load

* "fix decode bug"

* "follow commnet"

* "fix error"

* "fix hook bug"

* fix based comment

* fix copyright

* fix based on comment

* add copyright hook

* add copyright hook

* refine copyright hook

* "test copyright hook"

* fix check style

* fix ci

In the original util.cmake. enable_virtualenv.c is always regenerated when cmake files are changed, which leads to the relinking of all the targets depends on paddle_utils.