Update mkdocs markdown extensions.

Author: jgebal

mkdocs.yml

@@ -1,5 +1,6 @@
 # Format documented here
 # http://www.mkdocs.org/user-guide/configuration/
+# https://squidfunk.github.io/mkdocs-material/getting-started/
 
 site_url: http://utPLSQL.org/
 site_name: utPLSQL
@@ -12,6 +13,7 @@ extra_css:
 theme:
   name: material
   palette:
+    # Palette toggle for light mode
     - media: "(prefers-color-scheme: light)"
       scheme: default
       toggle:
@@ -26,11 +28,10 @@ theme:
   logo: assets/icon-transparent.png
   favicon: assets/favicon.png
   features:
-    - navigation.instant  # disable for offline docs
+    - navigation.instant
     - navigation.indexes
     - navigation.tabs
     - navigation.tracking
-    - navigation.indexes
     - toc.follow
     - toc.integrate
     - search.suggest
@@ -61,6 +62,8 @@ markdown_extensions:
   - pymdownx.snippets
   - pymdownx.superfences
   - pymdownx.caret
+  - pymdownx.mark
+  - pymdownx.tilde
   - toc:
       permalink: true
 use_directory_urls: false