Added Middleware interface

Author: JulianFun123

src/main/java/org/javawebstack/httpserver/handler/Middleware.java

@@ -0,0 +1,5 @@
+package org.javawebstack.httpserver.handler;
+
+public interface Middleware extends RequestHandler {
+
+}

src/main/java/org/javawebstack/httpserver/router/annotation/DefaultValue.java

@@ -0,0 +1,5 @@
+package org.javawebstack.httpserver.router.annotation;
+
+public @interface DefaultValue {
+    String value();
+}