'histogram' approximates a distribution calculation by counting the number
of times samples fall into pre-configured bins. This implementation does not
require bins to be equally sized. The user must specify upper bounds on bins
Bounds. The implementation includes a +Inf bound automatically.
Storage cost is proportional to the number of bins. The implementation is biased in favor of writes.
A binning histogram of unequal, pre-defined bins
Struct to implement Iterator over Histogram
The upper bound for each