Include comments in PO.Item output

Fixes #5

lib/po.js

@@ -192,6 +192,12 @@ PO.Item.prototype.toString = function () {
         return lines;
     };
 
+    if (this.comments.length > 0) {
+        this.comments.forEach(function (c) {
+            lines.push('# ' + c);
+        });
+    }
+
     if (this.references.length > 0) {
         this.references.forEach(function (ref) {
             lines.push('#: ' + ref);

test/write.js

@@ -38,6 +38,13 @@ describe('Write', function () {
         assertHasLine(str, "msgstr \"Source\"");
     });
 
+    it('write translator comment', function () {
+        var input = fs.readFileSync(__dirname + '/fixtures/comment.po', 'utf8');
+        var po = PO.parse(input);
+        var str = po.toString();
+        assertHasLine(str, "# Comment");
+    });
+
     describe('msgctxt', function () {
         it('should write context field to file', function () {
             var input = fs.readFileSync(__dirname + '/fixtures/big.po', 'utf8');