Lazy SMP

Start all threads searching on root position and
use only the shared TT table as synching scheme.

It seems this scheme scales better than YBWC for
high number of threads.

Verified for nor regression at STC 3 threads
LLR: -2.95 (-2.94,2.94) [-3.00,1.00]
Total: 40232 W: 6908 L: 7130 D: 26194

Verified for nor regression at LTC 3 threads
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 28186 W: 3908 L: 3798 D: 20480

Verified for nor regression at STC 7 threads
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 3607 W: 674 L: 526 D: 2407

Verified for nor regression at LTC 7 threads
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 4235 W: 671 L: 528 D: 3036

Tested with fixed games at LTC with 20 threads
ELO: 44.75 +-7.6 (95%) LOS: 100.0%
Total: 2069 W: 407 L: 142 D: 1520

Tested with fixed games at XLTC (120secs) with 20 threads
ELO: 28.01 +-6.7 (95%) LOS: 100.0%
Total: 2275 W: 349 L: 166 D: 1760

Original patch of mbootsector, with additional work
from Ivan Ivec (log formula), Joerg Oster (id loop
simplification) and Marco Costalba (assorted formatting
and rework).

Bench: 8116244

src/search.h

@@ -88,6 +88,7 @@ struct LimitsType {
   std::vector<Move> searchmoves;
   int time[COLOR_NB], inc[COLOR_NB], npmsec, movestogo, depth, movetime, mate, infinite, ponder;
   int64_t nodes;
+  TimePoint startTime;
 };
 
 /// The SignalsType struct stores volatile flags updated during the search
@@ -101,12 +102,9 @@ typedef std::unique_ptr<std::stack<StateInfo>> StateStackPtr;
 
 extern volatile SignalsType Signals;
 extern LimitsType Limits;
-extern RootMoveVector RootMoves;
-extern Position RootPos;
 extern StateStackPtr SetupStates;
 
 void init();
-void think();
 void reset();
 template<bool Root> uint64_t perft(Position& pos, Depth depth);