* add multi-scale test

* Place mixed precision inside PaddleDetection

roll back to the monkey patch version as a temporary measure, before it is
merged into paddle

* Add command flag for `loss_scale`

* Fix a stupid indentation error

optimizer should be in the mixed precision context

* Initial FP16 training

* Add mixed precision training to rest of the detection models

* Revert "Add support for mixed precision training (#3406)"

This reverts commit 3a2c106271885071db7c0d85587540a8f83c24db.

* Bug fixes and some tweaks

* fix rpn_only in cascade mask fpn

* fix rpn_only in cascade rcnn

* refine cascade models

* cascade-mask-fpn add

* add rpn recall function and class-aware rpn

* Rename object_detection to PaddleDetection
* Small fix for doc