group init_xxx() functions in init_bitboard()
this may seem like the opposite of good programming practice, but the point is that the order in which initializations are done is important. leaving it to independant init_xxx() functions, gives the misleading impression that the order in which these functions are called is unimportant (a big mistake that has cost me some debugging time in the past).
remove PassedPawnMask[c][s] (unused)
move magics to separate file