Switched OpenCV to a 3-component version number.

Epoch is gone; now the version component names in C++ and CMake
are consistent (except REVISION corresponds to PATCH).
In OpenCVConfig.cmake.in, lowercased the commands in the example.

This is the preferred style nowadays, and more consistent with the
rest of the code.
In the example in OpenCVConfig.cmake.in, explicitly add the include paths.

After #1801, the include directories are no longer added automatically,
so we should show the user how to do that.
Merge pull request #1830 from SpecLad:config-includes
Merge pull request #1816 from SpecLad:no-more-epoch