Various improvements

context: fix memory free
subscribe: implement dummy methods
introspect: implement more
stream: keep track of dequeued buffers ourselves because we need to
be able to cancel and keep track of writable size.

src/context.c

@@ -260,7 +260,6 @@ static void context_free(pa_context *c)
 
 	if (c->proplist)
 		pa_proplist_free(c->proplist);
-	free(c);
 }
 
 void pa_context_unref(pa_context *c)