*   `hhtSparseSpectrum` added to *Numeric.HHT* module, for an alternate sparser
    representation of the Hilbert Spectrum.
*   `hhtDenseSpectrum` also added to *Numeric.HHT*, for an alternative denser
    representation.
*   `expectedFrequency` added to *Numeric.HHT* module, to calculate weighted
    average of frequency contributions at each step in time.
*   `dominantFrequency` also added to *Numeric.HHT* to calculate strongest
    frequency at each step in time.