SpecDistrWeight is an S4 class that implements a weighting function given
by
$$W_n(\alpha) := I\{\alpha \leq 0\}$$.
At position k the value \(W_n(2\pi (k-1)/n\) is
stored [in a vector values nested inside env] for k=1,...,T.
The number length(values) of Fourier frequencies for which
\(W_n\) will be evaluated may be set on construction or updated when
evoking the method getValues.