Customize split layout

[reaperzn]

It would be really cool if you could specify the grid layout. Currently it seems that the layout will always be a max of 2 rows and balance the number of columns.

It would be nice to be able to specify something like: ./terminator-split 12 --rows 4 or ./terminator-split 12 --columns 2 or ./terminator-split --rows 4 --columns 6

[acudovs]

Current split algorithm is just recursion. We should use some tree algorithm to implement proposed feature.