add 'restrict-filenames' option (#348)

docs/configuration.rst

@@ -108,6 +108,24 @@ Description Directory path used as the base for all download destinations.
 =========== =====
 
 
+extractor.*.restrict-filenames
+------------------------------
+=========== =====
+Type        ``string``
+Default     ``"auto"``
+Example     ``"/!? ()[]{}"``
+Description Characters to replace with underscores (``_``) when generating
+            directory and file names.
+
+            Special values:
+
+            * ``"auto"``: Use characters from ``"unix"`` or ``"windows"``
+              depending on the local operating system
+            * ``"unix"``: ``"/"``
+            * ``"windows"``: ``"<>:\"\\|/?*"``
+=========== =====
+
+
 extractor.*.skip
 ----------------
 =========== =====

docs/gallery-dl.conf

@@ -9,6 +9,7 @@
         "skip": true,
         "sleep": 0,
         "user-agent": "Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0",
+        "restrict-filenames": "auto",
 
         "artstation":
         {