Migrate docs to antora

- First step of migration to antora by creating a structure
  which can be build locally.
- From docs to spring-security-kerberos-docs
- Gradle build handles needed docs logic, etc
- Relates #166

spring-security-kerberos-docs/modules/ROOT/examples/AuthProviderConfigTest.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2002-2015 the original author or authors.
+ *
+ * Licensed 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.springframework.security.kerberos.docs;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(locations= {"AuthProviderConfig.xml"})
+public class AuthProviderConfigTest {
+
+	@Test
+	public void configLoads() {}
+}