add navigation links for mustache specs

[pietroppeter]

being autogenerate it is very long and hard to navigate.
I should manually add internal links and table of contents (ideally I would want to try to come up with a mechanism to unescape the output - this might require the refactoring...).
it would be nice to have a floating element for back to top. first google resources for this:

• https://www.w3schools.com/howto/howto_js_scroll_to_top.asp
• https://help.pixpa.com/kb/add-a-floating-back-to-top-button/