[twibooru] add extractors for searches, galleries, and posts

(#2219)

docs/configuration.rst

@@ -2070,6 +2070,32 @@ Description
     You can use ``"all"`` instead of listing all types separately.
 
 
+extractor.twibooru.api-key
+--------------------------
+Type
+    ``string``
+Default
+    ``null``
+Description
+    Your `Twibooru API Key <https://twibooru.org/users/edit>`__,
+    to use your account's browsing settings and filters.
+
+
+extractor.twibooru.filter
+-------------------------
+Type
+    ``integer``
+Default
+    ``2`` (`Everything <https://twibooru.org/filters/2>`__ filter)
+Description
+    The content filter ID to use.
+
+    Setting an explicit filter ID overrides any default filters and can be used
+    to access 18+ content without `API Key <extractor.twibooru.api-key_>`__.
+
+    See `Filters <https://twibooru.org/filters>`__ for details.
+
+
 extractor.twitter.cards
 -----------------------
 Type