Allow to pass a 'seed' to RKISS

This somewhat simplifies the code.

Suggested by Lucas Braesch.

No functional change.

src/book.cpp

@@ -348,11 +348,7 @@ namespace {
 
 } // namespace
 
-PolyglotBook::PolyglotBook() {
+PolyglotBook::PolyglotBook() : RKiss(Time::now() % 10000) {}
-
-  for (int i = Time::now() % 10000; i > 0; i--)
-      RKiss.rand<unsigned>(); // Make random number generation less deterministic
-}
 
 PolyglotBook::~PolyglotBook() { if (is_open()) close(); }
 

src/rkiss.h

@@ -61,17 +61,15 @@ class RKISS {
     return s.d = e + s.a;
   }
 
-  // Init seed and scramble a few rounds
+public:
-  void raninit() {
+  RKISS(int seed = 73) {
 
     s.a = 0xf1ea5eed;
     s.b = s.c = s.d = 0xd4e12c77;
-    for (int i = 0; i < 73; i++)
+    for (int i = 0; i < seed; i++) // Scramble a few rounds
         rand64();
   }
 
-public:
-  RKISS() { raninit(); }
   template<typename T> T rand() { return T(rand64()); }
 };