Add createDispatcherServlet hook point

Add an extra hook point in `AbstractDispatcherServletInitializer` to
customize the `DispatcherServlet`.

Issue: SPR-13222

src/asciidoc/web-mvc.adoc

@@ -205,7 +205,7 @@ based equivalent of the above `web.xml` example:
 
 `WebApplicationInitializer` is an interface provided by Spring MVC that ensures your
 code-based configuration is detected and automatically used to initialize any Servlet 3
-container. An abstract base class implementation of this interace named
+container. An abstract base class implementation of this interface named
 `AbstractDispatcherServletInitializer` makes it even easier to register the
 `DispatcherServlet` by simply specifying its servlet mapping.
 See <<mvc-container-config,Code-based Servlet container initialization>> for more details.
@@ -4462,6 +4462,9 @@ The `isAsyncSupported` protected method of `AbstractDispatcherServletInitializer
 provides a single place to enable async support on the `DispatcherServlet` and all
 filters mapped to it. By default this flag is set to `true`.
 
+Finally, if you need to further customize the `DispatcherServlet` itself, you can
+override the `createDispatcherServlet` method.
+
 
 
 

src/asciidoc/whats-new.adoc

@@ -525,6 +525,8 @@ public @interface MyTestConfig {
 * When using GSON or Jackson 2.6+, the handler method return type is used to improve
   serialization of parameterized types like `List<Foo>`.
 * Default JSON prefix has been changed from "{} && " to the safer ")]}', " one.
+* Protected `createDispatcherServlet` method in `AbstractDispatcherServletInitializer` to further
+  customize the `DispatcherServlet` instance to use.
 
 === WebSocket Messaging Improvements