Python3 support, autopep8 formatting, fix for os.startfile()

[skypeachblue]

New pull request for the correct branch

Converted to Python3 Formatted the code with autopep8 os.startfile() is a windows-only function, I created the startfile() function which checks the platform and calls the correct function to make this work on Linux

Tested with the example files on Manjaro Linux Python 3.10

[sherlly]

Can you test this version on Python 3.8 or Python 3.6? I think they are more popular one for users.