Commented test with visual representations of the world/grid/board.
Backtracked on test which forces big steps.
Tests for a row and column of 3 live cells. Code evolving from returning
constant coordinates to returning an expression representing the
'middle' one.
Tests for row and column with four live cells in a line. Pattern
starting to emerge in production code.
Test for a row with 5 live cells in a line.
Created and tested a helper function for making a row of live cells.
Simplified code to a one liner which returns an array of live cell
coordinates after removing the first and last elements.
Diagonal 3, middle survives.