Consider a font substitution map for proprietary fonts

[ronaldtse]

For example, MS fonts.

On macOS without MS Office installed or on Linux, the Calibri and Cambria fonts won't be available, this means they won't be able to use the ISO layout.

There is a risk that the user may not want to accept the separate license agreements.

In this case, I think we should give the user two options:

1. Install the fonts using Fontist and agreeing to the MS provided license agreement.
2. Install substituting fonts that are openly licensed using Fontist. i.e. for Calibri => Carlito; Cambria => Caladea.

I think this needs to be done inside Metanorma setup.

What do you think?

Ping @Intelligent2013 @abunashir

[Intelligent2013]

Some thoughts:

1. I think we can't guarantee that all user-defined/installed fonts will be compatible with Apache FOP.
2. Some font can have sub-font and user should somehow to define it in fop config.
   It's very complicated to build user-friendly solution in command line setup.

May be it would be better to develop some Java GUI application to operate the fonts (check for Apache FOP compatible, set of glyphs, etc.) and produce a config for FOP. But it's no quick and simple solution, and it's a one more big project.