DATACASS-106 - Support persistence lifecycle callbacks.

We now support persistence lifecycle callbacks via Spring's ApplicationEvents. Events are fired upon select, insert, update, delete, and truncate statements. The following events are available:

* BeforeSaveEvent: Before inserting/updating a row in the database, via insert(…) and update(…).
* AfterSaveEvent: After inserting/updating a row in the database, via insert(…) and update(…).
* BeforeDeleteEvent: Before deleting row from the database, via delete(…) and truncate(…).
* AfterDeleteEvent: After deleting row from the database, via delete(…) and truncate(…).
* AfterLoadEvent: After retrieving a row from the database, via select(…), slice(…), and stream(…).
* AfterConvertEvent: After converting a row from the database to a POJO, via select(…), slice(…), and stream(…).

Original pull request: #123.

src/main/asciidoc/reference/mapping.adoc

@@ -582,3 +582,33 @@ Below is an example of a Spring `Converter` implementation that converts from a
 }
 ----
 
+
+[[cassandra.mapping-usage.events]]
+== Lifecycle Events
+
+Built into the Cassandra mapping framework are several `org.springframework.context.ApplicationEvent` events that your application can respond to by registering special beans in the `ApplicationContext`. By being based on Spring's application context event infrastructure this enables other products, such as Spring Integration, to easily receive these events as they are a well known eventing mechanism in Spring based applications.
+
+To intercept an object before it goes into the database, you'd register a subclass of `org.springframework.data.cassandra.core.mapping.event.AbstractCassandraEventListener` that overrides the `onBeforeSave` method. When the event is dispatched, your listener will be called and passed the domain object (Java entity).
+
+====
+[source,java]
+----
+public class BeforeSaveListener extends AbstractCassandraEventListener<Person> {
+  @Override
+  public void onBeforeSave(BeforeSaveEvent<Person> event) {
+    ... change values, delete them, whatever ...
+  }
+}
+----
+====
+
+Simply declaring these beans in your Spring `ApplicationContext` will cause them to be invoked whenever the event is dispatched.
+
+The list of callback methods that are present in AbstractMappingEventListener are:
+
+* `onBeforeSave` - called in `CassandraTemplate#insert(...)` and `#update(...)` operations *before* inserting/updating record in the database.
+* `onAfterSave` - called in `CassandraTemplate#insert(...)` and `#update(...)` operations *after* inserting/updating record in the database.
+* `onBeforeDelete` - called in `CassandraTemplate#delete(Object, QueryOptions)` and `#delete(Object)` operations *before* deleting record from the database.
+* `onAfterDelete` - called in `CassandraTemplate#delete(Object, QueryOptions)` and `#delete(Object)` operations *after* deleting record from the database.
+* `onAfterLoad` - called in `CassandraTemplate#select(...)`, `#slice(...)`, and `#stream(...)` methods after record is retrieved from the database.
+