updates to support building on windows

[fdncred]

closes #253 thanks to @petrochenkov's fix mentioned there.

I just switched the order of a few lines. I did not change any in the build.rs. The rust-toolchain.toml had to be updated to support this crate which won't compile in 1.56.1 any longer.

Caused by:
  package `os_str_bytes v6.2.0` cannot be built because it requires rustc 1.57.0 or newer, while the currently active rustc version is 1.56.1