Periodicity v1.0b1

Introduces:

• Wavelet Power Spectrum with PyWavelets (periodicity.spectral.wavelet)
• Empirical Mode Decomposition and the Hilbert-Huang Transform (periodicity.spectral.emd and periodicity.spectral.hht)
• Phase Dispersion Minimization (periodicity.spectral.pdm and periodicity.spectral.pdm2)
• Many other useful functions:
  • periodicity.utils.find_extrema
  • periodicity.utils.find_zero_crossings
  • periodicity.utils.get_envelope
  • periodicity.utils.get_noise

Also, various minor bugfixes and a first documentation release at https://periodicity.readthedocs.io