plugin: Add Plugin.broken decorator.

src/livestreamer/plugin/plugin.py

@@ -153,6 +153,24 @@ class Plugin(object):
 
         return stream_types
 
+    @classmethod
+    def broken(cls, issue=None):
+        def func(*args, **kwargs):
+            msg = (
+                "This plugin has been marked as broken. This is likely due to "
+                "changes to the service preventing a working implementation. "
+            )
+
+            if issue:
+                msg += "More info: https://github.com/chrippa/livestreamer/issues/{0}".format(issue)
+
+            raise PluginError(msg)
+
+        def decorator(*args, **kwargs):
+            return func
+
+        return decorator
+
     def streams(self, stream_types=None, sorting_excludes=None):
         """Attempts to extract available streams.