Better readability fortransformers (#46)

* Changes default transformers to static function to enable better readability while consuming them

* Uses static variables on extension instead of static functions

* make old api public to not break compatibility

Author: lightsprint09

JSONCodable/JSONTransformer.swift

@@ -47,3 +47,13 @@ public struct JSONTransformers {
         encoding: {dateTimeFormatter.string(from: $0)})
     #endif
 }
+
+public extension JSONTransformer {
+    static var stringToURL: JSONTransformer<String, NSURL>{
+        return JSONTransformers.StringToNSURL
+    }
+    
+    static var stringToDate: JSONTransformer<String, NSDate>{
+        return JSONTransformers.StringToNSDate
+    }
+}