message: Add windows to Travis CI build
  This requires us to switch to language:sh since Travis doesn't support
  language:cpp yet, and have essentially two separate scripts guarded with
  ifs to build on all platforms.
diff: -language: cpp
  +language: sh
  +
  os:
  - linux
  - osx
  -compiler:
  - - clang
  - - gcc
  + - windows
  matrix:
  exclude:
  - - os: osx
  - compiler: gcc
  + - os: windows
  + include:
  + - os: linux
  + env:
  + - CC=clang
  + - CXX=clang++
  + - os: windows
  + env:
  + - CMAKE_GENERATOR="Visual Studio 15 2017"
  + - os: windows
  + env:
  + - CMAKE_GENERATOR="Visual Studio 15 2017 Win64"
  script:
  - - make config=release
  - - make config=coverage test
  + - if [[ "$TRAVIS_OS_NAME" != "windows" ]]; then make config=release; fi
  + - if [[ "$TRAVIS_OS_NAME" != "windows" ]]; then make config=coverage test; fi
  + - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then PATH=$PATH:/c/Program\ Files/CMake/bin; fi
  + - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then cmake -G "$CMAKE_GENERATOR" -DBUILD_DEMO=ON; fi
  + - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then cmake --build . -- -verbosity:minimal; fi
  + - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then ./Debug/demo.exe demo/pirate.obj; fi
  -after_success:
  - - bash <(curl -s https://codecov.io/bash)
  +after_script:
  + - if [[ "$TRAVIS_OS_NAME" != "windows" ]]; then bash <(curl -s https://codecov.io/bash); fi
  