Add CI for Windows

[XVilka]

It will help to solve the

• keeping the support on the same level
• package artifacts for Windows distribution (as EXE or ZIP)

Related to #666

[ivg]

Probably we should consider Azure instead Travis. We need to evaluate Azure pipelines vs Github actions vs Travis vs DockerHub

[XVilka]

It boils down to solving z3 build on MinGW OCaml port:

• Try to use GitHub Actions #1115 (comment)
• fdopen/opam-repository-mingw@7ca1bb1

[ivg]

We can use Github Actions too for windows support, moreover I believe it would be more practical. And yes, it all distills to z3 and llvm dependencies.

[XVilka]

Note that Z3 package was fixed: https://github.com/fdopen/opam-repository-mingw/blob/opam2/packages/z3/z3.4.8.9/opam