Add available subtitle data to newznab output

This commit adds subtitles that are included in the spot in the output from newznab. This will be useful for future use to allow apps like couchpotatoserver or sickbeard to download spots only that have certain subtitles included. This eliminated the requirement to download subs separately which may or may not be available for a spot.

The output conforms to the newznab api. I might do a similar thing for the spoken language, but will complete subtitle support first. 

Please note: I have no experience in PHP yet. If you would like me to handle this differently please tell me!