set feed encoding to utf-8

macros.py

 # rss feed generation
 # -----------------------------------------------------------------------------
 
-_RSS = """<?xml version="1.0"?>
+_RSS = """<?xml version="1.0" encoding="UTF-8"?>
 <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
 <channel>
 <title>%s</title>