add text2jax delimiter setup in mathjaxhelper

docs/scripts/mathjaxhelper.js

 MathJax.Hub.Config({
   config: ["MMLorHTML.js"],
   jax: ["input/TeX", "output/HTML-CSS", "output/NativeMML"],
+  tex2jax: {
+    inlineMath: [ ['$','$'] ],
+    processEscapes: true
+  },
   extensions: ["MathMenu.js", "MathZoom.js"]
 });
+