Add MathML test support demo

This was based on [MDN}(https://developer.mozilla.org/en-US/docs/Web/MathML/Authoring#Fallback_for_Browsers_without_MathML_support) and have some changes compatibles with GitHub Pages.

**Warning**: the `mspace.html` demo not work properly due

~~~
Uncaught TypeError: Cannot call method 'appendChild' of null
~~~