Itempool-class
is a class to represent an item pool. This class is composed
of the collection of 'Item' class objects.
item_list
The list of items that are 'Item' class
misc
A list of additional parameters for the item pool. For example,
one can put the calibration date of the item pool as
misc = list(calibration_date = as.Date("2020-01-17"))
.