[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>

searx/data/engine_traits.json

@@ -1,4 +1,57 @@
 {
+  "arch linux wiki": {
+    "all_locale": null,
+    "custom": {
+      "title": {
+        "de": "Spezial:Suche",
+        "fa": "\u0648\u06cc\u0698\u0647:\u062c\u0633\u062a\u062c\u0648",
+        "ja": "\u7279\u5225:\u691c\u7d22",
+        "zh": "Special:\u641c\u7d22"
+      },
+      "wiki_netloc": {
+        "de": "wiki.archlinux.de",
+        "fa": "wiki.archusers.ir",
+        "ja": "wiki.archlinux.jp",
+        "zh": "wiki.archlinuxcn.org"
+      }
+    },
+    "data_type": "traits_v1",
+    "languages": {
+      "ar": "\u0627\u0644\u0639\u0631\u0628\u064a\u0629",
+      "bg": "\u0411\u044a\u043b\u0433\u0430\u0440\u0441\u043a\u0438",
+      "bs": "Bosanski",
+      "cs": "\u010ce\u0161tina",
+      "da": "Dansk",
+      "de": "Deutsch",
+      "el": "\u0395\u03bb\u03bb\u03b7\u03bd\u03b9\u03ba\u03ac",
+      "en": "English",
+      "es": "Espa\u00f1ol",
+      "fa": "\u0641\u0627\u0631\u0633\u06cc",
+      "fi": "Suomi",
+      "fr": "Fran\u00e7ais",
+      "he": "\u05e2\u05d1\u05e8\u05d9\u05ea",
+      "hr": "Hrvatski",
+      "hu": "Magyar",
+      "id": "Bahasa Indonesia",
+      "it": "Italiano",
+      "ja": "\u65e5\u672c\u8a9e",
+      "ko": "\ud55c\uad6d\uc5b4",
+      "lt": "Lietuvi\u0173",
+      "nl": "Nederlands",
+      "pl": "Polski",
+      "pt": "Portugu\u00eas",
+      "ru": "\u0420\u0443\u0441\u0441\u043a\u0438\u0439",
+      "sk": "Sloven\u010dina",
+      "sr": "\u0421\u0440\u043f\u0441\u043a\u0438 / srpski",
+      "sv": "Svenska",
+      "th": "\u0e44\u0e17\u0e22",
+      "tr": "T\u00fcrk\u00e7e",
+      "uk": "\u0423\u043a\u0440\u0430\u0457\u043d\u0441\u044c\u043a\u0430",
+      "zh": "\u4e2d\u6587\uff08\u7e41\u9ad4\uff09"
+    },
+    "regions": {},
+    "supported_languages": {}
+  },
   "bing": {
     "all_locale": null,
     "custom": {},