diffsptk version 3.0.0

What's Changed

• Support STRAIGHT in pitch_spec by @takenori-y in #117
• Refactoring by @takenori-y in #118

Breaking Changes

• The double argument in diffsptk.read has replaced with dtype
• The argument order has changed in the following classes:
  • MinimumPhaseImpulseResponseToCepstrum
  • NegativeDerivativeOfPhaseSpectrumToCepstrum
  • CepstralAnalysis
  • MelCepstralAnalysis
  • SecondOrderAllPassMelCepstralAnalysis
  • MelFilterBankAnalysis
  • MelFrequencyCepstralCoefficientsAnalysis
  • PerceptualLinearPredictiveCoefficientsAnalysis