Summary of changes

• Enforced consistent use of signing callbacks within the application. Any object that implements the signingCallback pattern for signing commits or tags should use the exact same callback type and with the same meaning. type SigningCallback = (content: string) => {| code: number, field?: string, signedData?: string |}; If the code is NodeGit.Error.CODE.OK or 0, the operation will succeed and at least signedData is expected to be filled out. If the code is a negative number, except for NodeGit.Error.CODE.PASSTHROUGH, the signing operation will fail. If the code is NodeGit.Error.CODE.PASSTHROUGH, the operation will continue without signing the object.

Merged PRs into NodeGit

• Use same API for signingCb in all places that can be crypto signed #1621