Add support for WPAY ID3 Tag (Payment Address)

WPAY/Payment tag is nice to have to point to donation pages or crypto addresses.
It is reminiscent to the equally under-utilized rel=payment microformat.

Recently, there was some discussion for supporting it for podcasters both on web page and within RSS feeds (my suggestion). The Overcast Podcast app, for example, added support. I think supporting it as an ID3 tag would be a nice companion to these other methods.

Official description:

WPAY
   The 'Payment' frame is a URL pointing at a webpage that will handle
   the process of paying for this file.