增加mx2Element，参数是file的方法接口

swiftCore/src/main/java/com/brilliance/swift/SwiftTransfer.java

@@ -217,4 +217,13 @@ public class SwiftTransfer {
     public static String mx2Element(String xmlStr) {
         return new Mx2ElementCreatorManager().mx2Element(xmlStr);
     }
+
+    public static String mx2Element(File file) {
+        try {
+           String xmlStr = FileUtils.readFileToString(file);
+            return mx2Element(xmlStr);
+        } catch (IOException e) {
+            throw new SwiftException(e.getMessage());
+        }
+    }
 }