subscript: replace Fraction class with std::ratio
subscript: replace Fraction class with std::ratio

std::ratio implements the num/denum fraction as a type. It did not
implement the apply(AndAdd) functions that I needed it for. But those
were easy to implement as non-member functions as well.

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,chr-engwer/Vc,chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc