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

unified init in 0.14.1

Bump to v0.14 (open-mmlab#580)

Bump to v0.13 (open-mmlab#529)

Bump to v0.12 (open-mmlab#455)