Ready for use mock

[ronanrodrigo]

It is nice to empower anyone to build their own mocks. But, I think that Frisbee must provide a ready for use mock. Something like that:

public class MockGetter<Entity: Decodable>: Getable {
    var resultOnComplete: Result<Entity>
    var didCallGet = false

    // ...

    public func get<Entity: Decodable>(url: String, onComplete: @escaping (Result<Entity>) -> Void) {
        didCallGet = true
        completionHandler(resultOnComplete)
    }
}