Added toString method for PO

lib/po.js

@@ -7,6 +7,13 @@ var PO = function() {
 };
 
 PO.prototype.save = function(filename, callback) {
+  fs.writeFile(filename, this.toString(), function(err){
+    if (err) throw err;
+    callback && callback();
+  })
+};
+
+PO.prototype.toString = function() {
   var lines = ['msgid ""', 'msgstr ""']
     , that = this;
 
@@ -22,10 +29,7 @@ PO.prototype.save = function(filename, callback) {
     lines.push('');
   });
 
-  fs.writeFile(filename, lines.join("\n"), function(err){
+  return lines.join("\n");
-    if (err) throw err;
-    callback && callback();
-  })
 };
 
 PO.load = function(filename, callback) {