(Untested) Now extracts name from torrent

On spec, the code now reads the torrent file to determine the name of
the contents file (used for creating a symlink to it).  This should
make it easier to generate torrents, as they don't need to be named
exactly as the contents any more.
Minor tweaks

Added licence and workflow.  Made main script abort if torrent not
found, and determined that getting the filename out of the torrent
didn't work quite right.