Address U. F. O. shortcomings.

This attempts to address a number of issues mentioned in #1653, specifically the dropping of version data, the changing of glif names, and the reversal of reference and anchor orders. It also enables layered U. F. O. output in certain limited contexts outside of the specification.

I noticed before that the capital height and x height for Source Sans Pro were considerably different from those produced by SFCapHeight and SFXHeight, which made me think that they might be different values.

@davelab6?