New function biperiodogram() for calculating the biperiodogram of real-valued time series.
New function kim_and_powers_model() for reproducing signals described in Kim and Powers (1979).
cross_bicoherence() now follow an alternative definition of (cross-)bicoherence due to Kim and Powers (1979).
New function mode_matching() for fitting cross-bicoherence's empirical null distribution by the mode-matching method of Schwartzman (2008).
New function three_channel_mode() for generating a simple example of multivariate time series.
New parameters mc and mc_cores of bicoherence(), bispectrum(), cross_bicoherence(), and cross_bispectrum() for parallel computation.