Fix pep2rss to include PEPs written in reStructuredText format (GH-632)

pep2rss.py

@@ -15,8 +15,10 @@ def firstline_startingwith(full_path, text):
             return line[len(text):].strip()
     return None
 
-# get list of peps with creation time (from "Created:" string in pep .txt)
+# get list of peps with creation time
+# (from "Created:" string in pep .rst or .txt)
 peps = glob.glob('pep-*.txt')
+peps.extend(glob.glob('pep-*.rst'))
 def pep_creation_dt(full_path):
     created_str = firstline_startingwith(full_path, 'Created:')
     # bleh, I was hoping to avoid re but some PEPs editorialize