[Refactor] formats: tiny bit of cleanup.

Additionally, `stringify`'s defaults get `format`, even though it isn't
necessary due to the line that assigns it to the internal options. This
way, however, things are a bit more internally consistent.

lib/formats.js

@@ -3,16 +3,24 @@
 var replace = String.prototype.replace;
 var percentTwenties = /%20/g;
 
-module.exports = {
-    'default': 'RFC3986',
-    formatters: {
-        RFC1738: function (value) {
-            return replace.call(value, percentTwenties, '+');
-        },
-        RFC3986: function (value) {
-            return String(value);
-        }
-    },
+var util = require('./utils');
+
+var Format = {
     RFC1738: 'RFC1738',
     RFC3986: 'RFC3986'
 };
+
+module.exports = util.assign(
+    {
+        'default': Format.RFC3986,
+        formatters: {
+            RFC1738: function (value) {
+                return replace.call(value, percentTwenties, '+');
+            },
+            RFC3986: function (value) {
+                return String(value);
+            }
+        }
+    },
+    Format
+);

lib/stringify.js

@@ -24,6 +24,7 @@ var pushToArray = function (arr, valueOrArray) {
 
 var toISO = Date.prototype.toISOString;
 
+var defaultFormat = formats['default'];
 var defaults = {
     addQueryPrefix: false,
     allowDots: false,
@@ -33,7 +34,8 @@ var defaults = {
     encode: true,
     encoder: utils.encode,
     encodeValuesOnly: false,
-    formatter: formats.formatters[formats['default']],
+    format: defaultFormat,
+    formatter: formats.formatters[defaultFormat],
     // deprecated
     indices: false,
     serializeDate: function serializeDate(date) {