Movecount pruning reduction logic

This patch refines search reduction logic in case the position is not a former PV node and is pruned based on move count.

passed STC
https://tests.stockfishchess.org/tests/view/5e8092bde42a5c3b3ca2ed35
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 78848 W: 15480 L: 15170 D: 48198
Ptnml(0-2): 1406, 9310, 17773, 9438, 1497

passed LTC
https://tests.stockfishchess.org/tests/view/5e80bb13e42a5c3b3ca2ed4b
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 86596 W: 11451 L: 11033 D: 64112
Ptnml(0-2): 624, 7993, 25687, 8329, 665

closes https://github.com/official-stockfish/Stockfish/pull/2605

Bench: 5138771

AUTHORS

@@ -1,4 +1,4 @@
-# List of authors for Stockfish, as of January 7, 2020
+# List of authors for Stockfish, as of March 30, 2020
 
 Tord Romstad (romstad)
 Marco Costalba (mcostalba)
@@ -123,6 +123,7 @@ Pasquale Pigazzini (ppigazzini)
 Patrick Jansen (mibere)
 pellanda
 Peter Zsifkovits (CoffeeOne)
+Praveen Kumar Tummala (praveentml)
 Rahul Dsilva (silversolver1)
 Ralph Stößer (Ralph Stoesser)
 Raminder Singh