Added webmention link type

src/main/java/net/fortuna/ical4j/extensions/link/Webmention.java

@@ -0,0 +1,21 @@
+package net.fortuna.ical4j.extensions.link;
+
+import net.fortuna.ical4j.model.LinkRelationType;
+import net.fortuna.ical4j.model.parameter.LinkRel;
+import net.fortuna.ical4j.model.property.Link;
+
+import java.net.URI;
+
+/**
+ * Identifies a target URI that supports the Webmention protocol. This allows clients that mention a resource in some
+ * form of publishing process to contact that endpoint and inform it that this resource has been mentioned.
+ * <p>
+ * See also <a href="https://www.iana.org/assignments/link-relations/link-relations.xhtml">Link Relations</a>
+ */
+public class Webmention extends Link {
+
+    public Webmention(URI uri) {
+        super(uri);
+        add(new LinkRel(LinkRelationType.webmention));
+    }
+}