Support Different OS File Separators

[zachsez]

Use the os.sep constant instead of hard coded / to support Windows execution.
From: prg = ./hello.py
To: prg = '.' + os.sep + 'hello.py'

Example of Issue

OS Docs

[kyclark]

Great point. Really WSL is required to effectively use the material. I've tried to use a Windows command line, and it's just nearly impossible to get things to work correctly, e.g., the shebang. I hate having to prefix my commands with "python" (or "python.exe" or "python3" or whatever). I strongly encourage Windows users to install WSL and perhaps use VS Code (you can type "code prg.py" on the command line to open the editor with that program!).