Computes the interquantile range of data at the given quantile value in O(N) time complexity. For example, using a quantile value of either 0.25 or 0.75 will give the interquartile range. (This is the default since it is apparently the most common interquantile range in common usage.) Using a quantile value of 0.2 or 0.8 will give the interquntile range.
If the quantile point falls between two indices, linear interpolation is used.
This function is somewhat more efficient than simply finding the upper and lower quantile and subtracting them.
Tip: A quantile of 0 or 1 is handled as a special case and will compute the plain old range of the data in a single pass.