start bitboard init (see commit details)

- bitboard.c: make attacks for knight/king
- square macros (BB, BBfile, BBrank) renamed sq_make, sq_file,
  sq_rank, moved to board.h (and become temporarily inline funcs)
- different macros/defs moved to "correct place" (bitboard/board/piece):
  board.[ch]: everything related to board/square
  bitboard.[ch]: everything related to bitboards
  piece.[ch]: everything related to pieces

test/bitboard-test.c

@@ -0,0 +1,23 @@
+//#include "debug.h"
+//#include "pool.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include "../src/bitboard.h"
+#include "../src/position.h"
+#include "../src/piece.h"
+//#include "../src/fen.h"
+
+int main(int __unused ac, __unused char**av)
+{
+    char str[128];
+    bitboard_init();
+    for (square_t sq = 0; sq < 64; ++sq) {
+        sprintf(str, "%2d %#lx %#lx knight", sq, sq_bb[sq], knight_attacks[sq]);
+        bitboard_print(knight_attacks[sq], str);
+        sprintf(str, "%2d %#lx %#lx knight", sq, sq_bb[sq], king_attacks[sq]);
+        bitboard_print(king_attacks[sq], str);
+    }
+    return 0;
+}