Make proportional font outputs work (when the MONO axis is set to <1)

[arrowtype]

Work to fix #24. More details in that issue.

• fix normal glyph widths in proportional outputs
• fix code ligature glyph widths in proportional outputs, if Code Ligatures: True is set in the config
• get kerning working when Code Ligatures: True is set in the config

For proportional fonts, kerning (and other OT features) now remains, even though code ligatures are updated from the dlig to calt feature tag.

Unfortunately, I’ve now realized that more feature code than is ideal gets replaced in MONO=1 fonts, but that was the case before, and it is substantially harder to change there, because the feature code has to be more radically altered. That is a different issue, though (#26).

[arrowtype]

As far as I can tell in my testing so far, this introduces only improvements, and no regressions. It may be slightly confusing that it changes the font family names from Rec Mono X to Rec Code X, however, and that these naming updates aren’t yet moved in the releases in the main Recursive project repo. So, I’ll wait until I’ve updated the main release before merging this.

If anyone wants proportional Rec Code fonts, however, the ones in this branch should be good to go!

[seankhl]

I used this branch to generate lighter-weight fonts (I find the defaults a bit to heavy), and so far it's working perfectly for me whereas with main I was having the same issues described in #24. Looking forward to seeing this merged and thanks for the beautiful and highly configurable font!

My only suggestion is to maybe tweak the naming so that if MONO is set to 0, the name isn't "Code" but maybe "Sans" or "UI" (in contrast to "Code") or something. But I get that this type of automagical behavior can be a bit confusing and hard to maintain... it's just that I am using the custom proportional fonts for UI rather than code so the naming is a bit off in my case.