v1.6.3

• eref formatting debug: metanorma/metanorma-bipm#41
• Language variant macros: metanorma/metanorma-iso#419
• Support lutaml macros—metanorma-plugin-lutaml gem: 279c2fe
• Rename ISO-Date footnote type to Unpublished-Status: metanorma/metanorma-iso#402
• Customise italicisation of mathml/mi: #367
• Processing of key definition lists: #202