Introduce Remote.IsSupportedUrl.
Fix xml doc related warnings
Introduce Repository.CherryPick.
Introduce PatchEntryChanges

Exposes same properties than TreeEntryChanges through composition
Cleanup DiffTreeToTreeFixture to use var and consts when appropriate
Use a callback for credentials

Instead of making the user choose beforehand, use a callback to let the
user ask a database or human about the credentials.

If desired, a hard-coded value can still be provided via a lambda, e.g.

    (_url, _user, _types) => new UsernamePasswordCredentials() { ... }
Hide GitCredentialType from API