Remove EventListener and IEvent marker interfaces

This allows Event Bus to interface with existing classes without
modification.

event-bus-core/src/test/java/dev/kske/eventbus/core/CancelTest.java

@@ -11,7 +11,7 @@ import org.junit.jupiter.api.*;
  * @author Leon Hofmeister
  * @since 0.1.0
  */
-class CancelTest implements EventListener {
+class CancelTest {
 
 	EventBus	bus;
 	int			hits;

event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java

@@ -10,7 +10,7 @@ import org.junit.jupiter.api.*;
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-class DispatchTest implements EventListener {
+class DispatchTest {
 
 	EventBus	bus;
 	static int	hits;
@@ -27,7 +27,7 @@ class DispatchTest implements EventListener {
 	}
 
 	/**
-	 * Tests {@link EventBus#dispatch(IEvent)} with multiple handler priorities, a subtype handler
+	 * Tests {@link EventBus#dispatch(Object)} with multiple handler priorities, a subtype handler
 	 * and a static handler.
 	 *
 	 * @since 0.0.1

event-bus-core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java

@@ -6,4 +6,4 @@ package dev.kske.eventbus.core;
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-public class SimpleEvent implements IEvent {}
+public class SimpleEvent {}