[emms-help] [patch] update to libtag info support

[Rasmus]

Hi,

The following patch makes some small changes to emms-info-libtag.el to
make it easier to customize. For instance, libtag handles wma files!
I also added another line to the c-program stderr.

One thing that might be worth considering is whether
`emms-info-libtag-known-extensions' should be a list rather than a
string. The regexp could then be computed.

Also, I did not get emms-print-metadata with my melpa package — not
even the source. I did not check if it's included with the ELPA
package since it is v3.

Cheers,
Rasmus