Add examples (apache#14)

* Create pulsar-functions module (#1)

* Create pulsar-functions module

* rename `sdk` package to `api`

* Added the first cut of the Java interface for Pulsar functions (#2)

* Added a simple example

pulsar-functions/api-examples/src/main/java/org/apache/pulsar/functions/api/examples/ExclamationFunction

@@ -0,0 +1,29 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.functions.api.examples;
+
+import org.apache.pulsar.functions.api.Context;
+import org.apache.pulsar.functions.api.RequestHandler;
+
+public class ExclamationFunction implements RequestHandler<String, String> {
+    @Override
+    public String handleRequest(String input, Context context) {
+        return input + "!";
+    }
+}