Enable code highlighting in docs

mkdocs.yml

@@ -1,2 +1,13 @@
 site_name: Gathio
-theme: material
+theme:
+    name: material
+    features:
+        - content.code.copy
+markdown_extensions:
+    - pymdownx.highlight:
+          anchor_linenums: true
+          line_spans: __span
+          pygments_lang_class: true
+    - pymdownx.inlinehilite
+    - pymdownx.snippets
+    - pymdownx.superfences