Localise italicisation preferences

Created by: opoudjis

This is a nice-to-have:

There are different conventions with regard to the italicisation of single-character mathematical variables, as documented in http://milde.users.sourceforge.net/LUCR/Math/math-font-selection.xhtml#math-style. They are supported in TeX as configuration options, through math-style:

• math-style=upright: never italic
• math-style=ISO: always italic
• math-style=TeX (default): Greek capital letters normal, lowercase Greek letters and Roman letters italic
• math-style=French: Greek capital letters normal, lowercase Greek letters normal, uppercase Roman letters normal, lowercase Roman letters italic

There are routine queries on tex.stackoverflow on journals wanting Uppercase Greek letters normal; and French practice is quite different to the default.

In MathML, these differences can be realised by inserting mi/@mathvariant='normal' as required, and that's what we have done in our stack using MathJax and jEuclid: https://github.com/metanorma/metanorma-standoc/issues/367. We will continue to do so, and the default italicisation behaviour of MathML, which MathJax implements, is not a blocker to us.

But I think it would be useful if these divergences in default italicisation from the MathML default could be specified as configuration options in MathJax, rather than requiring intervention with the MathML source.