vs2019
------

* The :generator:`Visual Studio 16 2019` generator was added.  This is
  experimental and based on "Visual Studio 2019 Preview 2" because this
  version of VS has not been released.

  The VS 2019 generator differs from generators for earlier versions
  in that it does not provide variants that specify the target platform
  in the generator name.  Instead :variable:`CMAKE_GENERATOR_PLATFORM`
  must be used, e.g. through the ``-A`` command-line option.  Furthermore,
  the default target platform (architecture) is now based on the *host*
  platform.  The VS host toolset selection is now based on the host
  architecture as well.
