Feature: windows support

[2285f5b](https://github.com/informalsystems/modelator-py/commit/2285f5b57427f5b7b4acd7eb81d73a5cb0bc0fcc) only explicitly supports unix like OS's but _perhaps_ some effort should be invested to support windows too.

Supporting three OS's is a lot of work though and requires rigorous testing.

Start by reviewing commit 2285f5b and identifying the Unix-specific assumptions it introduced. Define the required Windows behavior and testing approach before changing anything; done means the utility works on Windows as well as Unix-like systems with rigorous coverage.

Written by the indexing model from the issue text.