Provide Windows CI script

[lemire]

We could possibly add appveryor CI testing with an .appveyor.yml file that looks like the following... we need to validate that CMake builds work under Windows.

version: '{build}'
branches:
  only:
  - master
image:
    - Visual Studio 2017
    - Visual Studio 2015
clone_folder: c:\projects

platform:
- x64

environment:
  matrix:
    - GENERATOR: "Visual Studio 15 2017" # x86 build
      AVXFLAG: "OFF"
    - GENERATOR: "Visual Studio 15 2017 Win64" # x64 build
      AVXFLAG: "OFF"
    - GENERATOR: "Visual Studio 15 2017 Win64" # x64 build
      AVXFLAG: "ON"
    - GENERATOR: "Visual Studio 14 2015" # x86 build
      AVXFLAG: "OFF"
    - GENERATOR: "Visual Studio 14 2015 Win64" # x64 build
      AVXFLAG: "OFF"
    - GENERATOR: "Visual Studio 14 2015 Win64" # x64 build
      AVXFLAG: "ON"


matrix:
    fast_finish: true
    exclude:
      - image:      Visual Studio 2015
        GENERATOR: "Visual Studio 14 2015 Win64" 
        AVXFLAG: "ON"
      - image:      Visual Studio 2015
        GENERATOR: "Visual Studio 15 2017" # x86 build
      - image:      Visual Studio 2015
        GENERATOR: "Visual Studio 15 2017 Win64" # x64 build
      - image:      Visual Studio 2017
        GENERATOR: "Visual Studio 14 2015" # x86 build
      - image:      Visual Studio 2017
        GENERATOR: "Visual Studio 14 2015 Win64" # x64 build

build_script:
  - mkdir build
  - cd build
  - ps: cmake -G "$env:GENERATOR" -DFORCE_AVX="$env:AVXFLAG" ..
  - cmake --build .
  - ctest --verbose