spin direction
Hi, it would be useful to be able to control spin direction. In e.g. `bx-sync` case the spin looks silly since it's going in a direction opposite to the arrows:

![](https://user-images.githubusercontent.com/617641/111848549-9907c180-890b-11eb-8c06-4000dfe45b7f.gif)

I thought I could change it using `bx-flip-horizontal` but that does not work.