Hinting of variable fonts will not match static fonts

I believe I have finally reached the end of a long road VTT hinting Open Sans VF. Here are some fun facts.

First off, pixel deltas in variation CVTs are not possible. The method is to open the variation CVT window, choose a variation, and apply the delta as you would to a standard CVT...only this is just for font unit deltas. Those are only really appropriate for stem weights, really, and even then it's a bit fidgety. So, as far as heights not matching between the VF and static fonts currently served, nothing further can be done to improve it at this time. (With some time, I can maybe write some functions to help us out, but I'd have to see what the variation support in functions is like.)

Personally, I think that we should just back away from this and call it finished until there are improvements to VTT (and, ultimately, hinting bytecode). Mike @ MS says this is unlikely in the near future, and, really, that makes sense: with DirectWrite, this level of granular control is not often necessary.

Second, DWrite is also a reason why I say we should let this be. There are some stem weight issues on a handful of glyphs at a couple sizes, and individual glyph deltas aren't something @davelab6 wants me to spend time on. The percentage of browsers out there old enough to not use DWrite is less than 1%. Everything else is fine. Let's not worry about tweaking things for ClearType ever again. 🎉

Now then, between this and #11, we are going to break the internet. I don't know what to say to that.