Embed creates a new commit on top of another one.

PrefixTree creates a git tree containing the tree th at path prefix.

Push implements `git pull`.

PullOnce implements `git pull` without creating a new remote entry.

Push implements `git push`.

PushOnce implements `git push` without creating a new remote entry.

Address points to a branch in a networked git repo.

AuthManager provides authentication methods given a repo URL.

TTLManager provides TTL hints given a repo URL.