sfeed_update: override parse() example                                  [11/17]

The default rule in sfeed_update is:

	# parse and convert input, by default XML to the sfeed(5) TSV format.
	# parse(name, feedurl, basesiteurl)
	parse() {
        	sfeed "$3"
	}

To support a different parser that outputs to RSS/Atom it can be overridden in
the sfeedrc configuration shellscript file.

	# parse(name, feedurl, basesiteurl)
	parse() {
	        case "$2" in
        	*://api.github.com/**)
                	github_json_to_atom | sfeed "$3";;
	        *://www.youtube.com/**)
        	        youtube_with_duration "$2";;
	        *)
        	        sfeed "$3";;
	        esac
	}

