Consider: Support nested block and flat call structure

[usr42]

Support nested block and flat call structure with invoke method (see Kotlin in Action 11.3.3).

            KPact.consumer("Some Consumer").hasPactWith("Some Provider") {
                given("a certain state on the provider") {
                    whenever("a request for something").withPath("/hello") {
                        method("POST")
                        body("{\"name\": \"harry\"}")
                    } thenRespondWith {
                        status(200)
                        body("{\"hello\": \"harry\"}")
                    }
            }

vs

            KPact.consumer("Some Consumer").hasPactWith("Some Provider")
                    .given("a certain state on the provider").whenever("a request for something")
                    .withPath("/hello") {
                        method("POST")
                        body("{\"name\": \"harry\"}")
                    } thenRespondWith {
                        status(200)
                        body("{\"hello\": \"harry\"}")
                    }
            }

[usr42]

Now that I see the example, I don't like it.