v2.7.0

• Continuation of the significant plotting overhaul:
  • ftype and ttype for frequency and time axes labels
  • frequency labels: ‘fmid’, ‘fmin’, ‘f’, ‘px’
  • time labels: ‘same’, ‘trel’, ‘px’
  • swap_axes parameter to put frequency on the y-axis
• Add new Frame objects; Spectrum and TimeSeries
• Refactor spectrogram integration functions, and adding stg.spectrum and stg.timeseries)
• Move to np.random.default_rng for more robust random seeding
• Update tests