Add Jackson ServiceLoader support (closes #19). (#20)

Author: PascalSchumacher

src/main/resources/META-INF/services/com.fasterxml.jackson.databind.Module

@@ -0,0 +1 @@
+org.openapitools.jackson.nullable.JsonNullableModule

src/test/java/org/openapitools/jackson/nullable/JsonNullJacksonServiceLoadingTest.java

@@ -0,0 +1,13 @@
+package org.openapitools.jackson.nullable;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import junit.framework.TestCase;
+
+public class JsonNullJacksonServiceLoadingTest extends TestCase {
+
+    public void testJacksonJsonNullableModuleServiceLoading() {
+        String foundModuleName = ObjectMapper.findModules().get(0).getModuleName();
+        assertEquals(new JsonNullableModule().getModuleName(), foundModuleName);
+    }
+}