Put the current volume into context based on the standard deviation of volume and the average to turn absolute volume into a z-score of volume.
Has a parameter "skip_current" which if true only compares the prior close to the standard deviation/average - at open you'll obviously see very little volume, so it's kind of meaningless at that point.
It has a flaw: I am not removing the latest close from the series that the standard deviation and average are computed on. Not sure exactly how I should approach that and I think it won't change the result too severely so long as the length setting is reasonably high.
e:
Updated to avoid arithmetic overflow, which can occur for some data series, especially when the volume tends to report "0".
