Documentation is generated automatically during build/install process
Added check of minimum Doxygen version.
Install process causes generation of Overview documentation (unless already generated) by checking of occt_logo.png file existing.
Overview project regenerates documentation if any source file was changed.
Generation of OCCT overview documentation added as building of "Overview" project.
BUILD_OCCT_OVERVIEW variable introduced to offer generation OCCT overview documentation in html format.
Overview md files added to overview OCCT project.
"Building with CMake" article updated; overview.html copy into an install directory.
CMAKE_BUILD_TYPE for single-configuration generators described; BUILD_CONFIGURATION removed.
