The class tt(Screening) handles the screening parameters. Screening parameters
are obtained from the tt(Scenario) object (cf. section ref(SCENARIO)).

At construction time the following parameters are obtained:
    itemization(
    it() the probability that a case attends a screening: probability and
        distribution are specified like this:
       verb(
    #                   value   distribution:
    attendanceRate:     0.8     Normal
       )

    it() the screening rounds specify the screening ages and the modalities
        that are used for those rounds. Currently the modalities tt(MRI,
        Mammo) (mammography) and tt(Tomo) (tomosynthesis) are available.
        Screening rounds use specifications like this:
       verb(
    screeningRound:     58  Mammo MRI
       )
       Information about these rounds is stored in its tt(d_roundVect) vector,
        containing tt(Round) objects. Each tt(Round) object contains the
        round's age, the indices of the specified modalities and the names
        (IDs) of the specified modalities.
    )

Its member tt(radiationRisk) returns a vector of tt(double) values for each
(integral) age. It uses the bi-rad indices which are recomputed for each new
case (cf. section ref(GENCASES)) and consequently it is called by
tt(Loop::genCases) for each similated case.
