* add ext ops, support parrots
* fix lint
* fix lint
* update op from mmdetection
* support non-pytorch env
* fix import bug
* test not import mmcv.op
* rename mmcv.op to mmcv.ops
* fix compile warning
* 1. fix syncbn warning in pytorch 1.5
2. support only cpu compile
3. add point_sample from mmdet
* fix text bug
* update docstrings
* fix line endings
* minor updates
* remove non_local from ops
* bug fix for nonlocal2d
* rename ops_ext to _ext and _ext to _flow_warp_ext
* update the doc
* try clang-format github action
* fix github action
* add ops to api.rst
* fix cpp format
* fix clang format issues
* remove .clang-format
Co-authored-by: Kai Chen <chenkaidev@gmail.com>