* [Refactor] Use mdformat instead of markdownlint to format markdown.
* Update unavailiable api links in tutorials
* Update CONTRIBUTING.md
* Use mdformat==0.7.9 to support Python 3.6
* Add cosine cool down lr updater
* Use ema hook
* Update decay mult
* Update configs.
* Update T2T-ViT readme and format all readme
* Update swin readme
* Update tnt readme
* Add docstring for `CosineAnnealingCooldownLrUpdaterHook`.
* Update t2t readme and metafile
* add pth converter
* minor update on config files, add metafile and readme
* add missing readme and minor fixes
* minor fixes
* Update config names and checkpoint download link
* Update model_zoo.md
Co-authored-by: mzr1996 <mzr1996@163.com>