* Revise generator selection
If the host is x86, assume that msbuild is requested for windows.
If msbuild is requested and suitable, use it.
Else if a particular generator is requested, use it.
Else if ninja is available, use it.
Else on non-windows host, use "Unix Makefiles".
* Revise ninja_host detection
* Revise parallel configure detection
* Consolidate ninja path setup
* Update documentation
* Use portable chdir
* [ms-gltf] Use new generator selection
* Update versions
