- new sq_pinners
- new pseudo_is_legal() (unfinished)
- improve castling pseudo move gen
- more position and lower level bitboard helper funcs:
- pos_{_occ,between_occ,between_count,pinners}
- bb_{rank,file,rel_rank,_sq_aligned,_sq_between)
- rename some bitboard globals
- replace bb ranks/files enums with defines (issue with clang)
-> Need to find a way to use enum safely
- tests:
- add common-test.h
- new attack-test.c
- add many "const" in func parameters
- attack.c: sq_attackers()
- move print_board_raw from position.c to to board.c
- move some fen_check() tests to pos_check()
- add REL_RANK() macro. TODO: add one more for bitboards
- fen.c: more tests for FEN validity
- position.c: add pos_checkers() and pos_check()
- tests: add common-test.h (for shared FEN positions access)
