Add audio playback with mailcap and mpv

Allow audio to also be listened to from an email. Did not include setsid because then there would be no way to pause.

share/mailcap

@@ -3,6 +3,7 @@ text/html; openfile %s ; nametemplate=%s.html
 text/html; lynx -assume_charset=%{charset} -display_charset=utf-8 -dump %s; nametemplate=%s.html; copiousoutput;
 image/*; openfile %s ;
 video/*; setsid mpv --quiet %s &; copiousoutput
+audio/*; mpv %s ;
 application/pdf; openfile %s ;
 application/pgp-encrypted; gpg -d '%s'; copiousoutput;
 application/pgp-keys; gpg --import '%s'; copiousoutput;