add css property aspect-ratio

[xaddict]

To maybe get this picked up fast:
https://tomhodgins.github.io/aspect-ratio-spec/aspect-ratio.html

[Ugoku]

You realize that's not an official spec but just someone with a cool idea, right?

[xaddict]

yes. but sometimes putting things on here, or at least talking about it, speeds up the process of actual spec writing and implementation :)

[cvrebert]

Relevant: w3c/csswg-drafts#1173

[asimqt]

https://drafts.csswg.org/css-sizing-4/#ratios

[Schweinepriester]

On caniuse via MDN: https://caniuse.com/#feat=mdn-css_properties_aspect-ratio

In Chrome Canary 84.0.4145.0: https://twitter.com/Una/status/1260980901934137345

[mahboubii]

@Fyrd should aspect-ratio be added to this repo features since tools like doiuse relies on this? any automated script to pull info from MDN or should it be manual?