Complete refactoring for rktplayer, in order to make it play on DLNA renderers and also use UpNP media server resources.

library/base/tag-data-provider.rkt

@@ -0,0 +1,10 @@
+#lang racket/base
+
+(require racket/class)
+
+(provide tag-data-provider%)
+
+(define tag-data-provider%
+  (class object%
+    (abstract get-tag-data)
+    (super-new)))