Add feature: playlist downloading
Fix playlist downloading exceptions.

Changed parameter of `addID3` to title instead of index. Removed index counter `i` in `downloadSongs`. Changed `downloadSong` to `downloadSongs`
Fix playlist DL exceptions. Changed  parameter to  from , to use song title instead of index integer.
Merge branch 'sets' of https://github.com/RossHamish/Soundcloud-Downloader into sets
Merge pull request #9 from RossHamish/sets

Add feature: playlist downloading - RossHamish