table of contents now generate readable header IDs

src/lib/table-of-contents.svelte

@@ -33,10 +33,15 @@
         return document.querySelectorAll("h2, h3, h4, h5");
     }
 
+    // Generates an ID for a given header node. Does not override
+    // any existing ID.
     let getHeaderId = function(header: Node): string {
         var id = (header as HTMLElement).id;
+        
         if (!id) {
-            id = `header-${idCounter}`;
+            var text = (header as HTMLElement).innerText.toLowerCase();
+            text = text.replaceAll(/[^a-zA-Z0-9]/gi, "-");
+            id = text;
             (header as HTMLElement).id = id;
             idCounter += 1;
         }