Ending game automatically when statis is reached

plus properly seeding math/rand and swapping the chars used for grid to
better match black/white from canonical example.

conway/go/conways-game-of-life/main.go

@@ -29,15 +29,27 @@ func main() {
 		os.Exit(2)
 	}
 
+	cksum := game.Checksum()
+
 	ticks := time.Tick(time.Duration(*sleepMs) * time.Millisecond)
 	generations := 0
 	for now := range ticks {
 		fmt.Printf("\nGeneration %v\n%v\n", generations, now)
 		fmt.Println(game)
+
 		game.EvaluateGeneration()
+
+		if cksum == game.Checksum() {
+			fmt.Println("Stasis!")
+			os.Exit(0)
+		}
+
+		cksum = game.Checksum()
+
 		if *mutate && generations%2 == 0 {
 			game.Mutate()
 		}
+
 		generations++
 	}
 }