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.

[Zeecka]

  File "/home/user/Desktop/PCRT.py", line 68
    except IOError,e:
           ^^^^^^^^^
SyntaxError: multiple exception types must be parenthesized