Streamline build process and fix incompatible masters

[rschiang]

Currently, Crimson Pro doesn’t build against the latest version of fontTools and thus impossible to contribute further changes. After fighting with the confusing error messages of fontTools for a few days, I finally figured out the release-blocking issues in the repository.

Here’s the to-do list breakdown and my current progress:

• removing large binaries from repo ✅
  Proofs are still accessible through Git history. Font files could be uploaded through “Releases”.

• change interpolation weight of semibold to 500 ⚠️ ^(needinfo)
  Required by fonttools to have a “base master” instance that isn’t interpolated, see varLib.models locations parameter - how does it work? fonttools/fonttools#1943.

  To elaborate: The current “Regular” master has a weight of 500, but none of the instances have this weight value; the closest would be Semibold, which has an interpolation weight of 509. This breaks a lot of assumptions from Google Fonts’ own toolchain, including floating-point rounding errors.

• fix incompatible masters on currency glyphs 🔜 ^(WIP)
  There seems to be some unfinished alternative glyphs that is breaking the build.

  I’ve successfully fixed all of them on my experimental fork (scaled 114% to match other fonts’ em-height), and I’ll produce a version on the vanilla Crimson Pro in the next few days:
  

• update readme and build instructions

There are still a few glitches that I’m working on (e.g. colonsign breaks interpolation), but I’m gonna start a pull request first to keep track of the progress. Please let me know if there are any questions!