Association rule mining.

`min-confidence` is the minimum confidence of rules.
`tree` is the FP-tree.

Frequent item set mining based on the FP-growth algorithm.

`min-support` is the required minimum support of item sets in terms of frequency.
`itemsets` is the item set database. Each row is an item set, which may have
different length. The item identifiers have to be in [0, n), where n is the
number of items. Item set should NOT contain duplicated items.

Builds an FP-tree.

`min-support` is the required minimum support of item sets in terms of frequency.
`supplier` is a supplier that returns a stream of item sets. Each item set
may have different length. The item identifiers have to be in [0, n),
where n is the number of items. Item set should NOT contain duplicated items.