This class contains an array-like structure which holds two vectors of same
length.
fValVector holds parameter values (class border) and
fDistVector holds the corresponding probabilities of the
cumulative distribution function. The user should enter items as pairs of
values and cumulative distribution densities (into a single vector which is
divided later).
The class width may differ!
next is supposed to return a continuous value to a given
empirical distribution (using linear interpolation as in piecewise linear
distribution).