Support for variable fonts

[elliottslaughter]

Thanks for supporting Brick! I've been using it for a long time, and have been consistently happy with it.

I'm wondering what the prospects might be for supporting variable fonts? Most browsers are now supported, and many fonts now provide variable support.

This isn't just a size optimization. E.g. Source Sans Pro has some oddly inconsistent weights, which make it difficult to get everything to look right.

Thanks!