[2chen] Add 2chen.moe extractor (#2707)

* [2chen] Add 2chen.moe extractor

* change "==" to is

* fix for "test_unique_pattern_matches"

* fix regex pattern and group matching

* fix regex again

* [2chen] add 'reply_no' and 'hash' metadata and change 'filename_fmt'

also made an entry in supportedsites.md

* [2chen] unescape 'title'

* [2chen] partition() -> rpartition()

* [2chen] extract 'date' and 'name' metadata

* [2chen] remove 'offset' argument

* [2chen] do some changes

* [2chen] do some more changes

* [2chen] unescape 'name' and 'filename'

gallery_dl/extractor/__init__.py

@@ -10,6 +10,7 @@ import re
 
 modules = [
     "2chan",
+    "2chen",
     "35photo",
     "3dbooru",
     "420chan",