Summary:
First commit contains the initial code from Richard's branch.
Second commit are the changes that I made during the writing process
Third commit is the update to support category/topic pair for each commit

Pull Request resolved: https://github.com/pytorch/pytorch/pull/47360

Reviewed By: ejguan

Differential Revision: D24741003

Pulled By: albanD

fbshipit-source-id: d0fcc6765968dc1732d8a515688d11372c7e653d