* Improve CPU features detection
CMAKE_SYSTEM_PROCESSOR is pretty useless (e.g. when compiling with
MSVC ARM64 toolchain and Ninja still returns system processor).
* Don't build src/utils targets by default
Fix compilation for UWP platform.
* Add more Visual studio Git ignore patterns
* Autogenerate Doxygen docs
- document version requirements in the top-level file.
- remove incorrect version requirements from sub-dirs.
- set min. required version to 3.5 in top-level file.
- set minimun required version to 3.9 under docs/ .
- make documents building an option (on by default.)
so, the tree can be built using cmake-3.5 using
-DBUILD_DOCS=0 on the command line.