Don't ignore --max-size when outputting to stdout

[makew0rld]

Why did I even do this? From the README CLI help:

  -m, --max-size string        Set the file size limit. Any download that exceeds this size will
                               cause an Info output and be deleted.
                               Leaving it blank or setting to zero bytes will result in no limit.
                               This flag is ignored when outputting to stdout.
                               Format: <num> <optional-byte-size>
                               Examples: 423, 3.2KiB, '2.5 MB', '22 MiB', '10gib', 3M

The Info should be outputted to stderr, and gemget should exit with a non-zero exit code.