I'm surprised there are no comments here about the code! It looks like the characters of the font are specified programmatically on top of a self-contained glyph-drawing library, all written in a custom Lisp dialect ("patel") running on top of node, written by the same author as the font. Really impressive!
https://github.com/be5invis/Iosevka/tree/master/glyphs
https://github.com/be5invis/Iosevka/tree/master/support
https://github.com/be5invis/patel