GitLab

* fix dpool

* add _pair in dpool func

* Update deform_conv_cuda.cpp

* Update deform_pool_cuda.cpp

* fix the imports in __init__.py

* update contribution guide

* restructure the ops directory

* add some repr strings

* Implement all extension building in main setup.py

* Remove old build files

* Adapt installation guide

* Refactor to comply with flake8

* Move imports into functions & refactor module paths

* Format setup.py with yapf

* Move cython/numpy import back to head of file

* Add note to use verbose mode for pip in INSTALL.md

* Reformat use yapf 0.27.0

* Add yapf style file

Fixed error `TypeError: super(type, obj): obj must be an instance or subtype of type` .