Move documents to a sub-directory

to support multi-language selector.

docs/overrides/javascripts/mathjax.js

@@ -0,0 +1,16 @@
+window.MathJax = {
+  tex: {
+    inlineMath: [["\\(", "\\)"]],
+    displayMath: [["\\[", "\\]"]],
+    processEscapes: true,
+    processEnvironments: true,
+  },
+  options: {
+    ignoreHtmlClass: ".*|",
+    processHtmlClass: "arithmatex",
+  },
+};
+
+document$.subscribe(() => {
+  MathJax.typesetPromise();
+});