Speed up kpk initialization

The trick is to classify more position at first cycle,
so to reduce following work. Speed up is of about 50% !

Also some cleanup while there.

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

src/main.cpp

@@ -39,7 +39,7 @@ using namespace std;
 
 extern bool execute_uci_command(const string& cmd);
 extern void benchmark(int argc, char* argv[]);
-extern void init_kpk_bitbase();
+extern void kpk_bitbase_init();
 
 int main(int argc, char* argv[]) {
 
@@ -52,7 +52,7 @@ int main(int argc, char* argv[]) {
   // Startup initializations
   init_bitboards();
   Position::init();
-  init_kpk_bitbase();
+  kpk_bitbase_init();
   init_search();
   Threads.init();