[2chen] implement generic 2chen board extractors

support
- https://sturdychan.help/
- https://schan.help/ (#8680)

docs/supportedsites.md

@@ -19,12 +19,6 @@ Consider all listed sites to potentially be NSFW.
     <td>Boards, Threads</td>
     <td></td>
 </tr>
-<tr id="2chen" title="2chen">
-    <td>2chen</td>
-    <td>https://sturdychan.help/</td>
-    <td>Boards, Threads</td>
-    <td></td>
-</tr>
 <tr id="35photo" title="35photo">
     <td>35PHOTO</td>
     <td>https://35photo.pro/</td>
@@ -1274,6 +1268,22 @@ Consider all listed sites to potentially be NSFW.
     <td></td>
 </tr>
 
+<tr id="2chen" title="2chen">
+    <td colspan="4"><strong>2chen Instances</strong></td>
+</tr>
+<tr id="sturdychan" title="sturdychan">
+    <td>Sturdychan</td>
+    <td>https://sturdychan.help/</td>
+    <td>Boards, Threads</td>
+    <td></td>
+</tr>
+<tr id="schan" title="schan">
+    <td>Schan</td>
+    <td>https://schan.help/</td>
+    <td>Boards, Threads</td>
+    <td></td>
+</tr>
+
 <tr id="blogger" title="blogger">
     <td colspan="4"><strong>Blogger Instances</strong></td>
 </tr>