[mod] Archlinux Wiki: improved request API & upgrade to data_type: traits_v1

re-implementation of the Archlinux Wiki:

- fetch_traits(): fetch languages, wiki URLs and title arguments
- add content field to the result list
- add documentation

Wikis from wiki.archlinux.fr, wiki.archlinux.ro, archtr.org/wiki do no longer
exists (has been merged in the main wiki).

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/src/searx.engine.archlinux.rst

@@ -0,0 +1,9 @@
+.. _archlinux engine:
+
+==========
+Arch Linux
+==========
+
+.. automodule:: searx.engines.archlinux
+  :members:
+