Move pawn and material tables under Thread class

This change allows to remove some quite a bit of code
and seems the natural thing to do.

Introduced file thread.cpp to move away from search.cpp a lot
of threads related stuff.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/material.cpp

@@ -85,7 +85,7 @@ namespace {
 
 /// MaterialInfoTable c'tor and d'tor allocate and free the space for Endgames
 
-MaterialInfoTable::MaterialInfoTable() { funcs = new Endgames(); }
+void MaterialInfoTable::init() { Base::init(); funcs = new Endgames(); }
 MaterialInfoTable::~MaterialInfoTable() { delete funcs; }