**Eight queens**

This program solves the well known problem of the eight
queens on a board. The problem is placing eight chess queens
on the chessboard in a way that no queen can attack any of the
other queens... in other words there must be no two queens on
the same row, the same coloumn or the same diagonal.

The program generates the list of all possible solutions in
which every solution is represented by an 8-digit numbers
where every digit is between 1 and 8. The n-th digit tells
on what columns should be placed the queen on the n-th row.