It would be nice to be able to "fill" down or right
(and maybe up or left as well) similar to Excel.
Basically you could select a start cell and a block of
adjacent cells and then use <ctl-d> to fill down,
<ctl-r> to fill right, etc. Filling copies the value
in the start cell to the other cells selected.
Migrated to: https://github.com/bpangburn/swingset/issues/9