run-time variables for referencing current row and column in cell

[zerg000000]

provide run-time variables like current row and column in cell to support something like formula.

e.g.

......
    sheet("some cal") {
       1..30 { i ->
           row { cell( i , '<---my number' ) }
        }
        row { cell( "=${cur.col}0:${cur.col}${cur.row}", '<--total sum formula' ) } // output should be =A1:A30
    }