quick-element docs and demo

!f[](//i.imgur.com/ewdY65H.png) Bad quick-element:
asdf
!f[:img](https://i.imgur.com/ewdY65H.png)
!f[:video](//i.imgur.com/QSgq4k1.mp4){autoplay=true controls=true}
!f[hyperfiddle.ui/img](https://i.imgur.com/ewdY65H.png){}
!f[hyperfiddle.ui/img]("https://i.imgur.com/ewdY65H.png"){}

quick-element-sugar

![](//i.imgur.com/ewdY65H.png)
![:img](https://i.imgur.com/ewdY65H.png)
![:video](//i.imgur.com/ewdY65H.mp4)
![hyperfiddle.ui/img](https://i.imgur.com/ewdY65H.png)