Minor code tweaks
Changes in the infrastructure: storage.js now supports requesting multiple files; the main peerflix module is now just a torrent downloader, which can be initialized without a server
A massive re-work that allows Peerflix to be used to download one or more files from a torrent regularly. In comparison with part-file, the new storage system maps the local files to the actual byte range of the file in the torrent, rather than the piece range, which means that files are now saved properly to disk. This is still rather untested, but it seems to work