Add -q --quiet flag for disabling prints and warnings

Would be a nice addition on top of #11, to allow for commands such as `rsid3 -q --TIT2 file.mp3` if only exit status is needed. Of course, `rsid3 --TIT2 file.mp3 >/dev/null 2>&1` is also possible, but less elegant. Plus, with `-q` there would be opportunity for micro-optimization, since the intent that no prints are needed is communicated to the program.