Color or CBDT/CBLC support

[noraj]

I was using asciidoctor-pdf but I had a blocking error (asciidoctor/asciidoctor-pdf#2448) due to ttfunk.

It's different form #45 as in both cases I was using a TTF font and not an OTF font. However, is looks similar to #81.

I know very little about fonts but I can read this on the ArchLinux Wiki:

Emoji fonts come in different formats: CBDT/CBLC (Google), SBIX (Apple), COLR/CPAL (Microsoft), SVG (Mozilla/Adobe).

Among the TTF fonts Noto Color Emoji and JoyPixels are using CBDT/CBLC format, Twemoji is available as CBDT/CBLC format or SVG (SVG in OTF, so SVG format is not TTF) format and Symbola is outline only (grayscale).

I'm not really sure if it's a matter of color / grayscale or a matter of format.

[pointlessone]

Unfortunately TTFunk (and Prawn by proxy) doesn't support any of those tables (not CB*, not SVG). At the moment there's only support for basic outlines.