Allow event handlers with non-void return type

Also removed unnecessary files from the Event Bus Proc JAR and
configured GPG signing as well as deployment to Sonatype OSSRH.

event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java

@@ -6,17 +6,10 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
 import java.lang.annotation.*;
 
 /**
- * Indicates that a method is an event handler. To be successfully used as such, the method has to
- * comply with the following specifications:
- * <ul>
- * <li>Specifying an event type by either
- * <ul>
- * <li>Declaring one object parameter</li>
- * <li>Defining the class of the event using the annotation value</li>
- * </ul>
- * </li>
- * <li>Return type of {@code void}</li>
- * </ul>
+ * Indicates that a method is an event handler.
+ * <p>
+ * To be successfully used as such, the method has to specify the event type by either declaring one
+ * parameter of that type or setting the annotation value to the corresponding class.
  *
  * @author Kai S. K. Engelbart
  * @since 0.0.1

event-bus-core/src/main/java/dev/kske/eventbus/core/EventHandler.java

@@ -43,7 +43,7 @@ final class EventHandler implements Comparable<EventHandler> {
 		this.method		= method;
 		useParameter	= annotation.value() == USE_PARAMETER.class;
 
-		// Check for correct method signature and return type
+		// Check handler signature
 		if (method.getParameterCount() == 0 && useParameter)
 			throw new EventBusException(method + " does not define an event type!");
 
@@ -53,9 +53,6 @@ final class EventHandler implements Comparable<EventHandler> {
 		if (method.getParameterCount() > 1)
 			throw new EventBusException(method + " defines more than one parameter!");
 
-		if (!method.getReturnType().equals(void.class))
-			throw new EventBusException(method + " does not have a return type of void!");
-
 		// Determine handler properties
 		eventType	= useParameter ? method.getParameterTypes()[0] : annotation.value();
 		polymorphic	= method.isAnnotationPresent(Polymorphic.class);