Native MathML per Frédéric Wang

This add-on performs the following actions on each page to try and switch to native MathML rendering when possible:

- Insert CSS stylesheets to display the hidden MathML output generated by MediaWiki, MathJax ≥ 3 and KaTeX ≥ 0.2.

- Set the preference cookie of MathJax 2 so that it uses its NativeMML output processor.

It is recommended to install math fonts for best MathML rendering.

Examples of Web pages:
- Wikipedia Fourier transform (MediaWiki)
- KaTeX homepage (KaTeX)
- MathJax samples (MathJax 3)
- math.stackexchange (MathJax 2)