Support calculating based on fontSize

Capsize currently accepts inputs which act as constraints for the algorithm generating the styles. Primarily, those constraints are capHeight & leading*:

const styles = capsize({ fontMetrics, leading: 12, capHeight: 10 });

However, my project has a design which specifies a set of fontSize & lineHeight combos:

fontSize	lineHeight
12px	20px
14px	22px
20px	28px

I’d like to be able to use capsize to generate the correct style object given those inputs as constraints:

const styles = capsize({ fontMetrics, fontSize: 12, lineHeight: 20 });

I did a rough draft in https://github.com/seek-oss/capsize/pull/3, but it’s out of date and misses a few cases like snapping to grid.

---

* ^{(leading can also be specified as gap, but I’ll treat that as a variation of leading here)}

[michaeltaranto]

@apkoponen I caught up with @jesstelford and feel that the issues i found previously may no longer be a problem.

Planning to include fontSize support, just working on getting the package published and initial documentation first.

[michaeltaranto]

Thanks to @jesstelford for helping out, this is live on the site now 👏