Fix broken image links in reference documentation.

Resolves #1328.

Author: gregturn

src/main/asciidoctor/server.adoc

@@ -17,7 +17,7 @@ The server-side of Spring-WS is designed around a central class that dispatches
 
 The following sequence diagram shows the processing and dispatching flow of the `MessageDispatcher`:
 
-image::sequence.png[align="center"]
+image::images/sequence.png[align="center"]
 
 When a `MessageDispatcher` is set up for use and a request comes in for that specific dispatcher, the `MessageDispatcher` starts processing the request. The following process describes how `MessageDispatcher` handles a request:
 

src/main/asciidoctor/what-is-spring-ws.adoc

@@ -63,7 +63,7 @@ Spring-WS consists of a number of modules, which are described in the remainder
 
 The following figure shows and the dependencies between the Spring-WS modules. Arrows indicate dependencies (that is, Spring-WS Core depends on Spring-XML and the OXM module found in Spring 3 and higher).
 
-image::spring-deps.png[align="center"]
+image::images/spring-deps.png[align="center"]
 
 == Supported standards