Out: add printf like variants to the output commands
Out: add info and infof functions

These are helpful when unittesting, as you can easily mock them.
print turned out to be a bit tricky to mock even though it's
possible (see tests for Out.pm in t/02-out.t).
out.t: refactor unit tests for Out.pm
cmd::torrent: implement files only subcmd

When this is used, all files in the torrent that doesn't match
pattern are turned off, while those that match are turned on.
cmd::torrent: stop using printf directly