Calculate and return diagonal calculations for nth diagonal measures

[rs7q5]

Would like to return results on certain nth diagonals of a recurrence matrix.

tau_recurrence only calculates the average recurrence rate on the nth diagonal (averages the RR on the nth diagonal above and nth diagonal below), but I would like it to return these measures separately and maybe only up to the nth diagonal.

Other metrics at particular tau values like average diagonal length could also maybe be implemented.