credit Guido for his main script
refactor validate_board out of eight_queen
errors=5

for some reason, the solve_puzzle is broken
safely_put_one_more_queen is optimized:
- put only on position that least threathening
- take another optional argument which is scope of positions to find
- 6 tests fail
- can put up to 7 queens on the board without killing each other

Signed-off-by:  <>