[feat] engine: implementation of Anna's Archive

Anna's Archive [1] is a free non-profit online shadow library metasearch engine
providing access to a variety of book resources (also via IPFS), created by a
team of anonymous archivists [2].

[1] https://annas-archive.org/
[2] https://annas-software.org/AnnaArchivist/annas-archive

searx/settings.yml

@@ -297,6 +297,13 @@ engines:
     shortcut: 9g
     disabled: true
 
+  - name: anna's archive
+    engine: annas-archive
+    paging: False
+    categories: files
+    disabled: true
+    shortcut: aa
+
   - name: apk mirror
     engine: apkmirror
     timeout: 4.0