Feat user defined measures

[cezary986]

Users can now define custom quality measures function and use them for: growing, pruning and voting. Defining quality measure function is easy and straightforward, see example below.

from rulekit.classification import RuleClassifier

def my_induction_measure(p: float, n: float, P: float, N: float) -> float:
    # do anything you want here and return a single float...
    return (p + n) / (P + N)

def my_pruning_measure(p: float, n: float, P: float, N: float) -> float:
    return p - n

def my_voting_measure(p: float, n: float, P: float, N: float) -> float:
    return (p + 1) / (p + n + 2)

python_clf = RuleClassifier(
    induction_measure=my_induction_measure,
    pruning_measure=my_pruning_measure,
    voting_measure=my_voting_measure,
)