sync metrics keys

adds "missing" alternate /a glyphs for superscript & subscript. Closes #456

tooling: simplify makefile by updating PATH (which is broken in macOS "make", so require GNU make on macOS)

fixes shape bug in U+0490 /Geupturn-cy. Closes #766

fixes bug with alternate /aturn glyphs in roman

reduce tail length of atail at 900 + more kerning

a.2 kerning

Adds character variant 16: Lower-case a with tail (roman only)

readme: add mention of "Raveo"

adds alternate tabular one without bottom stroke via cv15

readme

bump version

website: cache bust font-files/InterVariable.ttf used by glyph inspector

website: update calt example as NxN was removed in v4.1

v4.1