add footnote support

Author: mkalkbrenner

mkdocs.yml

@@ -33,8 +33,6 @@ extra_css:
 markdown_extensions:
   - toc:
       title: On this page
-  - attr_list
-  - tables
   - admonition
   - pymdownx.details
   - pymdownx.superfences
@@ -47,6 +45,7 @@ markdown_extensions:
       auto_append:
         - content_footer.md
   - pymdownx.keys
+  - pymdownx.extra
 
 theme:
   name: material
@@ -104,4 +103,4 @@ nav:
     - ppuc_hardware/opto_16.md
   - ZeDMD:
     - zedmd/index.md
-  - GitHub Repositories: github_repos.md
+  - GitHub Repositories: github_repos.md