[revision3] Add new extractor(closes #6388)

- revision3.com
- testtube.com
- animalist.com

youtube_dl/extractor/__init__.py

@@ -557,6 +557,7 @@ from .redtube import RedTubeIE
 from .regiotv import RegioTVIE
 from .restudy import RestudyIE
 from .reverbnation import ReverbNationIE
+from .revision3 import Revision3IE
 from .ringtv import RingTVIE
 from .ro220 import Ro220IE
 from .rottentomatoes import RottenTomatoesIE