A unicode library which can be upgraded to the latest unicode rules, even on old Julia versions. Why do this? I want to resolve some JuliaSyntax compatibility issues mentioned at JuliaLang/JuliaSyntax.jl#381

The interface here is an amalgamation of Julia's Unicode stdlib and the functions from Base's strings/unicode.jl. The implementation is a Julia port of the C library utf8proc which has traditionally powered Base's unicode functionality.

Ideally I (Claire) hope this library might become the implementation of the Unicode stdlib and the Base functions from strings/unicode.jl, such as islowercase(), etc. But we'd need to figure out the implications of trying to make this upgradable without breaking how it's integrated into the Julia sysimage.