Add Windows builds using GitHub Actions

[NeroBurner]

Add VS 2017, VS 2019 and MinGW-w64 builds running the test cases. All
compiler have build jobs for C++11 and C++17.

Currently only the build-type 'Debug' is used, but can easily be
extended to build both 'Debug' and 'Release'.

• The Builds work fine based on v0.4.0
  • https://github.com/NeroBurner/glog/actions/runs/727394817
• All builds work on v0.5.0-rc1, but some tests fail
  • https://github.com/NeroBurner/glog/actions/runs/727397014
  • the VS 2019 builds and tests are green
  • VS 2017 test is failing
  • MinGW test is failing
• current master all jobs failing, some builds fail, some tests fail
  • https://github.com/NeroBurner/glog/actions/runs/727392380
  • VS 2017 and VS 2019 have some linker error during build
  • MinGW is failing the tests

---

related PR: #636

@sergiud please review

[sergiud]

Oh, wow, thank you. This looks great!

Nevermind the failing tests. That's fixable.