Add macros to simplify check for Vc 1.x vs 2.x
Add macros to simplify check for Vc 1.x vs 2.x

While looking at this, change the example in the documentation to show a
more useful version test.

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

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