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

src/perft.h

@@ -16,7 +16,7 @@
 
 #include "position.h"
 
-u64 perft(pos_t *pos, int depth, int ply, bool output);
+u64 perft(pos_t *pos, int depth,/* int ply,*/ bool divide);
 u64 perft_alt(pos_t *pos, int depth, int ply, bool output);
 
 #endif  /* PERFT_H */