Arrow bullet styles

Add right and left arrows as choices among the other bullet styles. Another option that would work as well for my purposes but that I think would be harder to implement is the ability to choose an emoji as bullet style.

Using Custom Rem-level formatting with tags, you can make this:

The usability is not perfect. You have to type the tag with ## or copy a tag with Ctrl + Shift + S and paste it onto a rem.

Once a few things get fixed it is also possible to build a tag applied to a parent which styles the bullets of all children.