Adjust volume of audio files to a standard level

Current version

normalize requires the following formula to be installed:
mad 0.15.1b MPEG audio decoder

Recent formula history

Viktor Szakats normalize: secure url(s)
Mike McQuaid Use hash rockets again. (#5177)
Mike McQuaid Use Ruby 1.9+ symbol hash keys in all formulae. (#4942)
Viktor Szakats normalize: use secure url (redirected to cleartext)
Viktor Szakats normalize: follow url redirect

Formula code at GitHub