Liblouis table for mathematical expressions in Dutch

[bertfrees]

[dkager]

• Liblouis table for Dutch Liblouis table for Dutch #6
• Validate existing conversion, removing and updating symbols.
• Convert symbols list into a liblouis table. Part of this goes into the Dutch table because it is not math-specific.
• Abstract rules from existing conversion.
• Add rules for spacing, etc.
• Move symbols, their substitutions and their descriptions into an XML file for use with pipeline-mod-braille.

[bertfrees]

(snaekobbi/sprints#100 (comment))

The rules for the output format (in Dutch) are here.