ability to autoplay ACTION_LAUNCH links

- needs a line in the rc file as
   "key Right = action auto"
   this autoplays the video when the right arrow key is pressed on
   a slide that contains and ACTION_LAUNCH link.
 - minor cleanup of link params handling
   now, the additional coordinaes are appended after handling the NULL case

I haven't put in the line required in the rc file directly into the config - I wasn't sure if you'd want that as a default.
Apologies about the config file though, I didn't realise I reindented stuff in it.