Convert git repo subhistory to a separate git repo

gistfile1.md

1. Clone

   git clone <remote-url> <dir>
   cd <dir>
   git remote rm origin

2. Find a start commit of your history

   START=git log | grep ...

3. Create new orphan branch

   git checkout --orphan new-root
   echo "This is a new repo" > README.md
   git commit -m "Initial commit" README.md

4. Rebase

   git rebase --onto new-root ${START}~ master

5. Cleanup & push

   git branch -D new-root
   git remote add origin <new-remote-url>
   git push origin master