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-proc/pom.xml

@@ -50,6 +50,21 @@
 						</goals>
 						<configuration>
 							<minimizeJar>true</minimizeJar>
+							<filters>
+								<filter>
+									<artifact>dev.kske:event-bus-core</artifact>
+									<excludes>
+										<exclude>META-INF/MANIFEST.MF</exclude>
+									</excludes>
+								</filter>
+								<filter>
+									<artifact>*:*</artifact>
+									<excludes>
+										<exclude>module-info.class</exclude>
+										<exclude>META-INF/maven/**</exclude>
+									</excludes>
+								</filter>
+							</filters>
 						</configuration>
 					</execution>
 				</executions>

event-bus-proc/src/main/java/dev/kske/eventbus/proc/EventProcessor.java

@@ -60,8 +60,6 @@ public class EventProcessor extends AbstractProcessor {
 					"Either the method or the annotation must define the event type");
 			else if (eventHandler.getParameters().size() > 1)
 				error(eventHandler, "Method must not have more than one parameter");
-			else if (eventHandler.getReturnType().getKind() != TypeKind.VOID)
-				error(eventHandler, "Method must return void");
 			else
 				pass = true;