GSoC 2020: OpenType support in FreeType

[Owen Lamb]

Hi Werner et al,

I've given Emmentaler an OpenType lookup subtable for stylistic alternates,
as the SMuFL specification suggests, and, as an experiment, I have
successfully encoded the two types of double whole note (breve), one as a
stylistic alternate of the other. However, LilyPond's current library for
reading music fonts, FreeType, doesn't seem to support OpenType layout
tables.

SMuFL's specification doesn't require a program to support OpenType
features. It states that a compliant font should also have some metadata
JSON files that describe the same stylistic alternate and ligature
information for such a program to read.

That said, it looks like I could go two ways. Would you rather I switch
FreeType for a font library with OpenType layout table support, or keep
FreeType and have LilyPond take what it needs from a SMuFL font's metadata
files?

(And of course, I might have missed something, so please let me know if I
did.)

Thanks,
Owen