bump to v2.7.0 (open-mmlab#4205)

* bump to v2.7.0

* update dates

* update version requirements

* rephrase

* resolve comments

Bump to v2.6.0 (open-mmlab#4038)

* bump to v2.6.0

* update version requirements

* Add README.md reference

* Fix README.md

Bump to v2.5.0 (open-mmlab#3879)

* bump to v2.5.0

* update PR

* resolve comments

* clean unnecessary modification

* update bc breaking

* rephrase bc-breaking

* rephrase

install wheel in github action (open-mmlab#3732)

Add metric items for COCO (open-mmlab#3497)

* Add metric iterms

* Fixed metric items

freeze version 2.2.1 (open-mmlab#3266)

Bump to 2.2 (open-mmlab#3170)

* Bump to 2.2

* remove some

* update

* update

* update mmcv version

Update mmcv requirement (open-mmlab#2949)

fix docstring styles (open-mmlab#2634)

release the last version of v1.x (open-mmlab#2617)