Introduce namespace Bitbases

Let's continue this namespace galore...

No functional change.

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

src/bitboard.h

@@ -25,8 +25,15 @@
 
 namespace Bitboards {
 
-extern void init();
-extern void print(Bitboard b);
+void init();
+void print(Bitboard b);
+
+}
+
+namespace Bitbases {
+
+void init_kpk();
+uint32_t probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
 
 }