add auto deep anchors / permalinks for headers

also add pilcrow permalinks

See:

* https://python-markdown.github.io/extensions/toc/
* https://docs.getpelican.com/en/latest/settings.html#basic-settings

Sorta related, not really, just saving for later:

* https://stackoverflow.com/questions/63788415/show-header-permalink-on-hover-pelican (that's about restructuredText, but there is some info about markdown, although it is incomplete as is leaves out defaults)
* getpelican/pelican-plugins#1397 (repo is deprecated)
* getpelican/pelican#2968 (added some helpful info for next person searching)

pelican/website/pelicanconf.py

@@ -78,3 +78,13 @@
 }
 
 TYPOGRIFY = True
+
+MARKDOWN = {
+    'extension_configs': {
+        'markdown.extensions.codehilite': {'css_class': 'highlight'},
+        'markdown.extensions.extra': {},
+        'markdown.extensions.meta': {},
+        'markdown.extensions.toc': {'permalink': True},
+    },
+    'output_format': 'html5',
+}