feat: change TOC plugin to tocbot (#774)

_javascript/modules/components/toc.js

@@ -0,0 +1,11 @@
+export function toc() {
+  // see: https://github.com/tscanlin/tocbot#usage
+  tocbot.init({
+    tocSelector: '#toc',
+    contentSelector: '.post-content',
+    ignoreSelector: '[data-toc-skip]',
+    headingSelector: 'h2, h3',
+    orderedList: false,
+    scrollSmooth: false
+  });
+}