Clones a subfolder into a new git repository.

.git_detach

git clone --no-hardlinks OLD_FLDR NEW_FLDR
cd NEW_FLDR
git filter-branch --prune-empty --subdirectory-filter ‘FLDR_TO_KEEP’ master
git remote rm origin
git update-ref -d refs/original/refs/heads/master
git reflog expire --expire=now --all
git repack -ad
git reset --hard
git gc --aggressive --prune=now