The class tt(AgeGroup) extracts age group specifications from the
configuration file. Age group specifications look like this:
        verb(
    0  - 40
    40 - 50
    50 - 60
    60 - 70
    70 - * 
        )
    which are half-open age ranges: tt([begin, end+CHAR41). The star 
specifies the maximum possible age (tt(MAX_AGE) as defined in tt(enums.h)).

    tt(AgeGroup) objects have two accessors: tt(beginAge), returning the begin
age, and tt(endAge) returning the ending age of the half open range.

When age groups are read then their ranges must connect. This is checked by
the member 
        verb(
    bool nextRange(std::vector<Type> const &vect, 
                    LineInfo const &lineInfo) const;
        )
    returning tt(true) if the begin age read from tt(lineInfo) equals the
end age in tt(vect.back()). This is used, e.g., when reading the age ranges of
the various breast densities (cf. tt(densities/add.cc)).
