Add extra detail on servlet listeners

Fixes spring-projectsgh-2518

Author: Dave Syer

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1271,7 +1271,8 @@ instance. By default the embedded server will listen for HTTP requests on port `
 
 [[boot-features-embedded-container-servlets-and-filters]]
 ==== Servlets and Filters
-When using an embedded servlet container you can register Servlets and Filters directly as
+When using an embedded servlet container you can register Servlets, Filters and all the 
+listeners from the Servlet spec (e.g. `HttpSessionListener`) directly as
 Spring beans. This can be particularly convenient if you want to refer to a value from
 your `application.properties` during configuration.
 
@@ -1280,9 +1281,10 @@ the case of multiple Servlet beans the bean name will be used as a path prefix.
 will map to `+/*+`.
 
 If convention-based mapping is not flexible enough you can use the
-`ServletRegistrationBean` and `FilterRegistrationBean` classes for complete control. You
-can also register items directly if your bean implements the `ServletContextInitializer`
-interface.
+`ServletRegistrationBean`, `FilterRegistrationBean` and
+`ServletListenerRegistrationBean` classes for complete control. You
+can also register items directly if your bean implements the
+`ServletContextInitializer` interface.