[Fontconfig] Variable fonts redux

[Lawrence D'Oliveiro]

I wrote:

> On Wed, 27 Sep 2017 18:58:41 -0400, Behdad Esfahbod wrote:
> 
>>   - Expose slant & italic standard axes as well, but Fontconfig
>> shoves FC_SLANT_ITALIC and FC_SLANT_OBLIQUE in the same element...
> 
> Do you want alternative noun forms? How about “italicity” and
> “obliquity”? Or even “lean”?

Oh, and of course “tilt”.

I’d even mention the sailing term “tack”, but that might be too
obscure...