Windows compatibility issue

[Dr. Sven Steffen Becker]

Multiprocessing on Windows uses a different process spawning mechanism and thus one cannot rely on visibility for global variables. Unix based processes always use forking as default process spawning.

[saviola777]

@sayan44 I've added Windows support (tested on Windows 7 with Python 3.8) in 9758bc8, please let us know if this doesn't work for you.