Add support for generating snippets in Markdown

This commit introduces support for generating snippets formatted
using Markdown. Asciidoctor remains the default.

A new SnippetFormat abstraction has been introduced with Asciidoctor
and Markdown implementations provided out of the box.
Markdown-formatted templates are also provided for all of the default
snippets.

Please refer to the updated reference documentation for further
details.

Closes gh-150
Closes gh-19

docs/src/test/java/com/example/mockmvc/CustomFormat.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2014-2016 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 com.example.mockmvc;
+
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.documentationConfiguration;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.restdocs.RestDocumentation;
+import org.springframework.restdocs.snippet.SnippetFormats;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.context.WebApplicationContext;
+
+public class CustomFormat {
+
+	@Rule
+	public final RestDocumentation restDocumentation = new RestDocumentation("build");
+
+	@Autowired
+	private WebApplicationContext context;
+
+	private MockMvc mockMvc;
+
+	@Before
+	public void setUp() {
+		// tag::custom-format[]
+		this.mockMvc = MockMvcBuilders.webAppContextSetup(this.context)
+				.apply(documentationConfiguration(this.restDocumentation)
+						.snippets().withFormat(SnippetFormats.markdown()))
+				.build();
+		// end::custom-format[]
+	}
+
+}