add repetition detection, root position count

- hist.c: add hist_next() - get next entry in history
- state_t: remove plycount, clock_50 -> ply50, add phase, repcount
- pos_t: add plycount, plyroot
- state_t moved to chessdefs.h
- perft-test: split perft from do_perft (todo for perft_alt)
- position.c: add pos_repcount()
- search.c: add is_draw()
- uci: set root position (after moves), adjust history moves repcount

Makefile

@@ -415,7 +415,7 @@ TEST          += movedo-test perft-test tt-test
 PIECE_OBJS    := piece.o
 FEN_OBJS      := $(PIECE_OBJS) fen.o position.o bitboard.o board.o \
 	hq.o attack.o hash.o init.o util.o alloc.o move.o \
-	eval.o eval-defs.o eval-simple.o
+	eval.o eval-defs.o eval-simple.o hist.o
 BB_OBJS       := $(FEN_OBJS)
 MOVEGEN_OBJS  := $(BB_OBJS) move-gen.o
 ATTACK_OBJS   := $(MOVEGEN_OBJS)