Unmix return and yield from from a single function

Fixes #453

Author: guicho271828

scholarly/_scholarly.py

@@ -305,6 +305,9 @@ def citedby(self, object: Publication)->_SearchScholarIterator:
             # Go one year at a time in decreasing order
             years = zip(range(year_end, year_low-1, -1), range(year_end, year_low-1, -1))
 
+        return self._citedby_long(object,years)
+
+    def _citedby_long(self, object: Publication, years):
         # Extract cites_id. Note: There could be multiple ones, separated by commas.
         m = re.search("cites=[\d+,]*", object["citedby_url"])
         pub_id = m.group()[6:]