Fix typo
Removing unused parameter
Only processing files with suffix '.mp3'

This makes the script more glob friendly.
Recurse down directories
Printing JSON for improved parsability

While `pprint` pretty much outputs JSON I'd rather be sure it's fully
compliant.
Making sure to close the file

We all have our pet peeves ;-)
Merge pull request #1 from JensRantil/minor-improvements

Minor improvements; Recurse, only MP3, print JSON