add fetch-specific request options

[Mouvedia]

redirect: "follow" | "error" | "manual"
referrer: "no-referrer" | "client" | URL
referrerPolicy: "no-referrer" | "no-referrer-when-downgrade" | "same-origin" | "origin" | "strict-origin" | "origin-when-cross-origin" | "strict-origin-when-cross-origin" | "unsafe-url"
integrity: String
keepalive: Boolean

cache will be covered by #4