Support `aspect-ratio` CSS property

[chungyc]

Add support for the aspect-ratio CSS property. It specifies a desired aspect ratio for a display element.

• auto
• ratios in the form of 1/1, 16/9, 2, or 0.5
• fallback values with auto and a ratio; e.g., auto 1/1 or 1/1 auto
• one of inherit, initial, revert, revert-layer, unset

I think we can support this by adding an aspectRatio function to Clay.Geometry. Its argument could be a Rational for ratios, a tuple of (auto, ratio) or (ratio, auto), or the usual set of auto, inherit, ... values. Its argument type could be a type class like AspectRatioValue, of which Rational and Value could be made instances. E.g.,

aspectRatio auto
aspectRatio initial
aspectRatio (16%9)
aspectRatio (16%9, auto)

This issue is mainly stating my intention to implement support for aspect-ratio and to track any work related to it, rather than a feature request for someone else to implement.

Note that this is distinct from the aspect-ratio media feature, which is already supported with Clay.Media.aspectRatio.

[turion]

That sounds like a great addition! Note that aspect-ratio: auto 3/4; is also valid CSS. Do you want to submit a PR?

[chungyc]

Do you want to submit a PR?

That's my plan ... eventually.