xi : arraylike of length N1
a sorted list of xcoordinates
yi : list of lists of length N1
yi[i] is the list of derivatives known at xi[i]
orders : list of integers, or integer
a list of polynomial orders, or a single universal order
direction : {None, 1, 1}
indicates whether the xi are increasing or decreasing
+1 indicates increasing
1 indicates decreasing
None indicates that it should be deduced from the first two xi
