[npr] Add extractor

removed md5 from _TEST

moved from xml data to json

test

changed _TEST url to one that will not expire, so tests would not be failing

youtube_dl/extractor/__init__.py

@@ -473,6 +473,7 @@ from .npo import (
     VPROIE,
     WNLIE
 )
+from .npr import NprIE
 from .nrk import (
     NRKIE,
     NRKPlaylistIE,