Keep marks after splitting a block (#1273)
Keep marks after splitting a block (#1273)

If you have, for example, a bold mark, and you hit "Enter", the new
block won't carry over the formatting. Instead, it should (at least if
you start typing right away).

Fixes #1269.
ashutoshrishi/slate,ianstormtaylor/slate,ianstormtaylor/slate,isubastiCadmus/slate