replace_metadata feature--allow regexp replacement of story metadata from ini.

plugin-defaults.ini

@@ -111,6 +111,20 @@ extratags: FanFiction
 ## epub by many readers).  Must be hex code, # will be added.
 background_color: ffffff
 
+## Use regular expressions to find and replace (or remove) metadata.
+## For example, you could change Sci-Fi=>SF, remove *-Centered tags,
+## etc.  See http://docs.python.org/library/re.html (look for re.sub)
+## for regexp details.
+## Make sure to keep at least one space at the start of each line and
+## to escape % to %%, if used.
+#replace_metadata:
+# Sci-Fi=>SF
+# Puella Magi Madoka Magica.* => Madoka
+# Comedy=>Humor
+# Crossover: (.*)=>\1
+# (.*)Great(.*)=>\1Moderate\2
+# .*-Centered=>
+
 ## Each output format has a section that overrides [defaults]
 [html]