wav_filter method to use strcasecmp instead of strcmp

[wvbraun]

Corrects the issue of using nested strcmp's to find a valid wav by instead using the cleaner strcasecmp method.

This is a simple fix intended to simply open some dialogue about contributing to the development of Tidal.

[yaxu]

thanks!

[wvbraun]

@yaxu do you have a channel on freenode, etc?

[yaxu]

@wvbraun We're active on #tidal and #tidalinnards on the TOPLAP slack http://toplap.org/toplap-on-slack/