Update HTTP request and response snippets to honour charset of content

Closes gh-126

spring-restdocs-core/src/test/java/org/springframework/restdocs/http/HttpRequestSnippetTests.java

@@ -84,7 +84,23 @@ public class HttpRequestSnippetTests {
 				.request("http://localhost/foo").method("POST").content("Hello, world")
 				.build());
 	}
+	
+	@Test
+	public void postRequestWithCharset() throws IOException {
+		this.snippet.expectHttpRequest("post-request-with-charset").withContents(
+				httpRequest(POST, "/foo")
+				.header(HttpHeaders.HOST, "localhost")
+				.header("Content-Type", "text/plain;charset=UTF-8").content(
+						"こんにちわ, 世界")); // Hello, World in japanese.
 
+		new HttpRequestSnippet().document(new OperationBuilder(
+				"post-request-with-charset", this.snippet.getOutputDirectory())
+				.request("http://localhost/foo").method("POST")
+				.header("Content-Type", "text/plain;charset=UTF-8")
+				.content("こんにちわ, 世界")
+				.build());
+	}
+	
 	@Test
 	public void postRequestWithParameter() throws IOException {
 		this.snippet.expectHttpRequest("post-request-with-parameter").withContents(

spring-restdocs-core/src/test/java/org/springframework/restdocs/http/HttpResponseSnippetTests.java

@@ -84,7 +84,15 @@ public class HttpResponseSnippetTests {
 		new HttpResponseSnippet().document(new OperationBuilder("response-with-content",
 				this.snippet.getOutputDirectory()).response().content("content").build());
 	}
-
+	
+	@Test
+	public void responseWithCharset() throws IOException {
+		this.snippet.expectHttpResponse("response-with-charset").withContents(
+				httpResponse(OK).header("Content-Type", "text/plain;charset=UTF-8").content("コンテンツ"));
+		new HttpResponseSnippet().document(new OperationBuilder("response-with-charset",
+				this.snippet.getOutputDirectory()).response().header("Content-Type", "text/plain;charset=UTF-8").content("コンテンツ").build());
+	}
+	
 	@Test
 	public void responseWithCustomSnippetAttributes() throws IOException {
 		this.snippet.expectHttpResponse("response-with-snippet-attributes").withContents(