Adding the possibility to skip pruning step when using CBA function

[DouglasMesquita]

Link to the issue

close #30

How to test the changes

data("iris")
formula <- Species ~ .

trans <- prepareTransactions(formula = formula, data = iris)
rulebase <- mineCARs(
  formula = Species ~ .,
  transactions = trans,
  supp = 0.05,
  conf = 0.9
)
n_rules <- length(rulebase)

cba_no_pruning <- CBA(formula, iris, supp = 0.05, conf = 0.9, pruning = NULL)

In this case, length(rules(cba_no_pruning)) == n_rules as desired.