Better "no content" support and polish in WebTestClient

The WebTestClient now takes advantage of the support for decoding
response to Void.class in WebClient so that applications can use
expectBody(Void.class) to the same effect as using
response.bodyToMono(Void.class) as documneted on WebClient#exchange.

The top-level, no-arg returnResult method (added very recently) has been
retracted, since the use of returnResult at that level, i.e. without
consuming the response content, should be used mainly for streaming.
It shouldn't be used for "no content" scenarios.

Documentation and Javadoc have been udpated accordingly.

src/docs/asciidoc/testing-webtestclient.adoc

@@ -50,7 +50,7 @@ Use this option to set up a server from a
 
 Internally the provided configuration is passed to `RouterFunctions.toWebHandler`.
 The resulting WebFlux application will be tested without an HTTP server using mock
-request and response objects
+request and response objects.
 
 
 [[webtestclient-context-config]]
@@ -171,7 +171,7 @@ You can go beyond the built-in assertions and create your own:
             });
 ----
 
-You can also exit the workflow and get an `ExchangeResult` with the response data:
+You can also exit the workflow and get a result:
 
 ----
     EntityExchangeResult<Person> result = client.get().uri("/persons/1")
@@ -190,6 +190,35 @@ instead of `Class<T>`.
 ====
 
 
+[[webtestclient-no-content]]
+=== No content
+
+If the response has no content, or you don't care if it does, use `Void.class` which ensures
+that resources are released:
+
+[source,java,intent=0]
+[subs="verbatim,quotes"]
+----
+    client.get().uri("/persons/123")
+            .exchange()
+            .expectStatus().isNotFound()
+            .expectBody(Void.class);
+----
+
+Or if you want to assert there is no response content, use this:
+
+[source,java,intent=0]
+[subs="verbatim,quotes"]
+----
+    client.post().uri("/persons")
+            .body(personMono, Person.class)
+            .exchange()
+            .expectStatus().isCreated()
+            .expectBody().isEmpty;
+----
+
+
+
 [[webtestclient-json]]
 === JSON content
 
@@ -225,22 +254,23 @@ You can also use https://github.com/jayway/JsonPath[JSONPath] expressions:
 === Streaming responses
 
 To test infinite streams (e.g. `"text/event-stream"`, `"application/stream+json"`),
-exit the response workflow via `returnResult` immediately after response status and
-header assertions, as shown below:
+you'll need to exit the chained API, via `returnResult`, immediately after response status
+and header assertions, as shown below:
 
 [source,java,intent=0]
 [subs="verbatim,quotes"]
 ----
-    FluxExchangeResult<Event> result = client.get().uri("/events")
+    FluxExchangeResult<MyEvent> result = client.get().uri("/events")
             .accept(TEXT_EVENT_STREAM)
             .exchange()
             .expectStatus().isOk()
-            .returnResult(Event.class);
+            .returnResult(MyEvent.class);
 
 ----
 
-Now you can use the `StepVerifier`, from the `reactor-test` module, to apply
-assertions on the stream of decoded objects and cancel when test objectives are met:
+Now you can consume the `Flux<T>`, assert decoded objects as they come, and then
+cancel at some point when test objects are met. We recommend using the `StepVerifier`
+from the `reactor-test` module to do that, for example:
 
 [source,java,intent=0]
 [subs="verbatim,quotes"]