Allow passing token for authentication

[jonathongardner]

Sometimes I don't want to store/pass my credentials to docker registry, It would be helpful if i could just pass the bearer token manually

DockerRegistry2.connect("https://registry", { bearer_token: "my-token" })

[deitch]

Interesting. connect() supports options, so that API already is there. You would need to add it to initalize to save it and then change doreq to use it properly.

Open to a PR on it.