synth: Data synthesis

Synthesise data matching spectral and covariance properties of a reference.

• match_spectra
  • match_spectra()
• match_covariance
  • match_covariance()
• match_reference
  • match_reference()
• match_cov_and_spectrum
  • match_cov_and_spectrum()
• synthesise_matched
  • synthesise_matched()
• synthesise_from_cov_and_spectrum
  • synthesise_from_cov_and_spectrum()