Polish contribution that added support for documenting HTTP headers

The main changes are:

- Update javadoc to align with changes made in 5a01016
- Update documentation with details of the new support for documenting
  HTTP headers
- Add tests to verify that HTTP headers are matched case-insensitively

Closes gh-71

docs/src/docs/asciidoc/documenting-your-api.adoc

@@ -288,6 +288,31 @@ built using one of the methods on `RestDocumentationRequestBuilders` rather than
 
 
 
+[[documenting-your-api-http-headers]]
+=== HTTP headers
+
+The headers in a request or response can be documented using `requestHeaders` and
+`responseHeaders` respectively. For example:
+
+[source,java,indent=0]
+----
+include::{examples-dir}/com/example/HttpHeaders.java[tags=headers]
+----
+<1> Perform a `GET` request with an `Authorization` header that uses basic authentication
+<2> Produce a snippet describing the request's headers. Uses the static `requestHeaders`
+method on `org.springframework.restdocs.headers.HeaderDocumentation`.
+<3> Document the `Authorization` header. Uses the static `headerWithName` method on
+`org.springframework.restdocs.headers.HeaderDocumentation.
+<4> Produce a snippet describing the response's headers. Uses the static `responseHeaders`
+method on `org.springframework.restdocs.headers.HeaderDocumentation`.
+
+The result is a snippet named `request-headers.adoc` and a snippet named
+`response-headers.adoc`. Each contains a table describing the headers.
+
+When documenting HTTP Headers, the test will fail if a documented header is not found in
+the request or response.
+
+
 [[documenting-your-api-constraints]]
 === Documenting constraints
 

docs/src/test/java/com/example/HttpHeaders.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2014-2015 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 com.example;
+
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.restdocs.headers.HeaderDocumentation.headerWithName;
+import static org.springframework.restdocs.headers.HeaderDocumentation.requestHeaders;
+import static org.springframework.restdocs.headers.HeaderDocumentation.responseHeaders;
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
+import static org.springframework.restdocs.mockmvc.RestDocumentationRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+public class HttpHeaders {
+
+	private MockMvc mockMvc;
+
+	public void headers() throws Exception {
+		// tag::headers[]
+		this.mockMvc
+				.perform(get("/people").header("Authorization", "Basic dXNlcjpzZWNyZXQ=")) // <1>
+				.andExpect(status().isOk())
+				.andDo(document("headers",
+						requestHeaders( // <2>
+								headerWithName("Authorization").description( 
+										"Basic auth credentials")), // <3>
+						responseHeaders( // <4>
+								headerWithName("X-RateLimit-Limit").description(
+										"The total number of requests permitted per period"),
+								headerWithName("X-RateLimit-Remaining").description(
+										"Remaining requests permitted in current period"),
+								headerWithName("X-RateLimit-Reset").description(
+										"Time at which the rate limit period will reset"))));
+		// end::headers[]
+	}
+}