Add WumpResponse#buffer

- Added a buffer function
- Add `WumpRequest#buffer` in typings

lib/model/WumpResponse.js

@@ -10,6 +10,10 @@ module.exports = class WumpResponse {
 	_addChunk (chunk) {
 		this.body = Buffer.concat([ this.body, chunk ]); 
 	}
+	
+	buffer () {
+		return this.body;	
+	}
 
 	text () {
 		return this.body.toString();
@@ -18,4 +22,4 @@ module.exports = class WumpResponse {
 	json () {
 		return JSON.parse(this.body);
 	}
-};
+};