simplify extractor constants

- single strings for URL patterns
- tuples instead of lists for 'directory_fmt' and 'test'
- single-tuple tests where applicable

gallery_dl/extractor/chan.py

@@ -16,7 +16,7 @@ class ChanThreadExtractor(Extractor):
     """Base class for extractors for Futaba Channel-like boards"""
     category = "chan"
     subcategory = "thread"
-    directory_fmt = ["{category}", "{board}", "{thread} - {title}"]
+    directory_fmt = ("{category}", "{board}", "{thread} - {title}")
     filename_fmt = "{tim}-{filename}.{extension}"
     archive_fmt = "{board}_{thread}_{tim}"
     api_url = ""