Simplify futility move count formula

Simpler formula but introduces some slight changes if d >= 10

Original code grows like  0.225 * d^1.8
New code grows like       0.222 * d^1.8

Full list of values:

d old new diff
--------------
0 2 2 0
1 2 2 0
2 3 3 0
3 4 4 0
4 5 5 0
5 6 6 0
6 7 7 0
7 9 9 0
8 11 11 0
9 13 13 0
10 15 16 1
11 18 19 1
12 21 21 0
13 24 24 0
14 27 28 1
15 31 31 0
16 35 35 0
17 39 38 -1
18 42 42 0
19 47 46 -1
20 51 51 0
21 55 55 0
22 60 60 0
23 65 65 0
24 70 70 0
25 75 75 0
26 81 80 -1
27 87 86 -1
28 92 91 -1
29 98 97 -1
30 104 103 -1
31 111 109 -2

Test code:

int main() {

  for(int d=0; d<32; d++)
  {
     int a = int(3 + 0.3 * pow(double(d), 1.8)) * 3/4 + (2 < d && d < 5);
     int b = int(2.4 + 0.222 * pow(d + 0.0, 1.8));

     std::cout << d << " " << a << " " << b << " " << b-a << std::endl;
  }

  return 0;
}

bench: 8350690

src/search.cpp

@@ -155,8 +155,8 @@ void Search::init() {
   // Init futility move count array
   for (d = 0; d < 32; ++d)
   {
-      FutilityMoveCounts[0][d] = int(3 + 0.3 * pow(double(d       ), 1.8)) * 3/4 + (2 < d && d < 5);
+      FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d +  0.0, 1.8));
-      FutilityMoveCounts[1][d] = int(3 + 0.3 * pow(double(d + 0.98), 1.8));
+      FutilityMoveCounts[1][d] = int(3.0 +   0.3 * pow(d + 0.98, 1.8));
   }
 }