parse url-anchor for time if it fits the pattern

This patch fixes https://github.com/klemens/ff-youtube-all-html5/issues/40.
It parses links of the sort <hours>h<minutes>m<seconds>s with all allowed omittances being accepted. Everything else is ignored. Probably not necessary, but can't hurt to be specific.

I tested it with the working version 2.1.3 distributed on the mozilla addon store (unpacked, changed, repacked).