Introduce 'follow up' moves

When we have a fail-high of a quiet move, store it in
a Followupmoves table indexed by the previous move of
the same color (instead of immediate previous move as
is in countermoves case).

Then use this table for quiet moves ordering in the same
way we are already doing with countermoves.

These followup moves will be tried just after countermoves
and before remaining quiet moves.

Passed both short TC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 10350 W: 1998 L: 1866 D: 6486

And long TC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 14066 W: 2303 L: 2137 D: 9626

bench: 7205153

src/search.h

@@ -41,6 +41,7 @@ struct Stack {
   SplitPoint* splitPoint;
   int ply;
   Move currentMove;
+  Move ttMove;
   Move excludedMove;
   Move killers[2];
   Depth reduction;