enhancement - added support for riff_wave (*.wav) audio files

git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@7723 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0
Merge branch 'master' of github.com:fieldtrip/fieldtrip