[refactor] add "Holiday" entity
[refactor] パターン別の計算を独立したCalculatorクラスに分けた
[refactor] Calculatorを束ねて祝日リストを作るCalculatorAggregate作成
[refactor] 一年分の祝日を算出するAnnualCalculatorとRepositoryを分離
[refactor] enable custom Calculator
[refactor] changed return value of CalculatorAggregate::computeDates() from DateTime to Holiday
Merge branch 'refactor'