Merge topic 'variables1'

9d20fe014f Help: moved 7 variables to "internal" section
dfb2d6178e Help: "internal variables" instead of "obsolete", with some explanatory prose
9c4cdc43f6 Help: declare CMAKE_HOME_DIRECTORY obsolete

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !2881