The following commands assume tracking remotes, eg:

$ git remote add -f haslett https://github.com/weavejester/haslett.git

Adding vendored libs

$ git subtree add --prefix vendor/haslett haslett master --squash

Updating from upstream

what's coming?

$ git fetch haslett
$ git diff-tree -p haslett/master vendor/haslett/

update

$ git subtree update --prefix vendor/haslett haslett master --squash
# provide descriptive commit message, eg: 'haslett v1.2'