Add support for status code 418 (#557)

lib/inc/drogon/HttpTypes.h

@@ -56,6 +56,7 @@ enum HttpStatusCode
     k415UnsupportedMediaType = 415,
     k416RequestedRangeNotSatisfiable = 416,
     k417ExpectationFailed = 417,
+    k418ImATeapot = 418,
     k421MisdirectedRequest = 421,
     k425TooEarly = 425,
     k426UpgradeRequired = 426,

lib/src/HttpUtils.cc

@@ -336,6 +336,11 @@ const string_view &statusCodeToString(int code)
             static string_view sv = "Expectation Failed";
             return sv;
         }
+        case 418:
+        {
+            static string_view sv = "I'm a Teapot";
+            return sv;
+        }
         case 421:
         {
             static string_view sv = "Misdirected Request";