Bump v0.21.1 (open-mmlab#1273)

* Bump v0.21.1

* add improvements in changelog

* add improvements in changelog

* fix cn readme

* change changelog

Bump v0.21.0 (open-mmlab#1258)

* change version to v0.21.0

* change version to v0.21.0

* change version to v0.21.0

* change version to v0.21.0

Bump v0.20.2 open-mmlab#1141

Bump to v0.20.1 (open-mmlab#1138)

* bump version 0.20.1

* bump version 0.20.1

Bump v0.20.0 (open-mmlab#1124)

* change version to v0.20.0

* change version to v0.20.0

* change version to v0.20.0

Bump v0.19.0 (open-mmlab#1009)

* change version to v0.19.0

* update changelog

Bump to v0.18.0 (open-mmlab#940)

* bump to v0.18.0

* replace \ with /

Bump to v0.17.0 (open-mmlab#841)

Bump to v0.16.0 (open-mmlab#749)

* Bump to v0.16.0

* fix doc

* fix changelog

* fix changelog

Bump to v0.15.0 (open-mmlab#669)

* Bump to v0.15.0

* fixed version