refactored static *requiredKeys sets, finished implementation of SingleFileTorrent
removed unused import in SingleFileTorrent.java
fully implemented SingleFileTorrent
fixed bug in BList which prevented reading of lists-within-lists
finished implementation of multi-file torrents
updated gitignore to include tests
Merge branch 'torrent-files'

Added updates -- implementations of the Torrent classes, including
checks and getters for the SingleFileTorrents