Force published field (#147)

* Force published field

When an atom item only have updated field, use it to fill published.

- Less function is using published field, it has to always been
populated.
- Simplify code when using both RSS and Atom feeds.

This fix #146

* Rename updated to published

following @Necoro comment

testdata/translator/atom/feed_item_updated_-_atom03_feed_entry_modified.json

@@ -2,7 +2,9 @@
     "items": [
         {
             "updated": "Thu, 01 Jan 2004 19:48:21 GMT",
-            "updatedParsed": "2004-01-01T19:48:21Z"
+            "updatedParsed": "2004-01-01T19:48:21Z",
+            "published": "Thu, 01 Jan 2004 19:48:21 GMT",
+            "publishedParsed": "2004-01-01T19:48:21Z"
         }
     ],
     "feedType": "atom",

translator.go

@@ -643,12 +643,20 @@ func (t *DefaultAtomTranslator) translateItemUpdatedParsed(entry *atom.Entry) (u
 	return entry.UpdatedParsed
 }
 
-func (t *DefaultAtomTranslator) translateItemPublished(entry *atom.Entry) (updated string) {
-	return entry.Published
+func (t *DefaultAtomTranslator) translateItemPublished(entry *atom.Entry) (published string) {
+	published = entry.Published
+	if published == "" {
+		published = entry.Updated
+	}
+	return
 }
 
-func (t *DefaultAtomTranslator) translateItemPublishedParsed(entry *atom.Entry) (updated *time.Time) {
-	return entry.PublishedParsed
+func (t *DefaultAtomTranslator) translateItemPublishedParsed(entry *atom.Entry) (published *time.Time) {
+	published = entry.PublishedParsed
+	if published == nil {
+		published = entry.UpdatedParsed
+	}
+	return
 }
 
 func (t *DefaultAtomTranslator) translateItemAuthor(entry *atom.Entry) (author *Person) {