[twitter] rename 'text-only' to 'text-tweets' (#570)

docs/configuration.rst

@@ -1715,14 +1715,14 @@ Description
     will be taken from the original Tweets, not the Retweets.
 
 
-extractor.twitter.text-only
----------------------------
+extractor.twitter.text-tweets
+-----------------------------
 Type
     ``bool``
 Default
     ``false``
 Description
-    Produce metadata for Tweets without media content.
+    Also emit metadata for text-only Tweets without media content.
 
     This only has an effect with a ``metadata`` (or ``exec``) post processor
     with `"event": "post" <metadata.event_>`_

docs/gallery-dl.conf

@@ -259,6 +259,7 @@
             "quoted": true,
             "replies": true,
             "retweets": true,
+            "text-tweets": false,
             "twitpic": false,
             "users": "timeline",
             "videos": true