v1.9.0

• Support sparse sources, i.e. source elements in Designspaces with a layerName attribute. Together with glyphsLib 3.2.0, this means automatic support for brace (and bracket) layers. Only outline and spacing information will be taken from sparse sources. Note that there's a bug in fontTools' MVAR generation code that is fixed upstream, but needs to be released (fonttools/fonttools#1477).
• Added a CLI option --expand-features-to-instances, useful when making static instances while using a shared feature file in the masters. The option will expand the feature file to all instances, to avoid inclusion problems with the include() statement.
• Support making variable CFF2 fonts in the future. This currently depends on fonttools/fonttools#1475.
• Bump minimum dependency versions to support the above.