Windows support

[ethanfrey]

Closes #28

Another try. I heard this is now supported with wasmer, but after building this (make docker-image-cross && make release), I get the following:

error: This crate doesn't yet support compiling on operating systems and architectures other than these:
       - FreeBSD and x86_64
       - FreeBSD and AArch64
       - macOS and x86_64
       - Linux and x86_64
       - Linux and AArch64
       - Android and x86_64
       - Android and AArch64
  --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/wasmer-singlepass-backend-0.17.0/src/lib.rs:23:1

Maybe it is "just" singlepass that doesn't support windows? Time for a ping

[webmaster128]

This work has been integrated in the meantime. See #389 for an overview of the state of Windows support.