update added ligatures to fira code v5

[jiyometrik]

fira code has had some significant updates since the current version used in this repo (v3), including infinites, more arrows, and more language-specific ligatures. will these be added to the ligaturizer script?

[ToxicFrog]

See #89; tl;dr Fira Code has completely changed the way the font works and handling that requires a significant redesign.