Permission error for log file

[wuffi]

Thanks a lot for writing and sharing this very nice and helpful software!

A potential caveat for new users is a permission problem for the log file when running rayoptics in a directory for which the user does not have write permissions:

(rayoptics) C:\Users>rayoptics
Traceback (most recent call last):
  File "C:\Users\user\Anaconda3\envs\rayoptics\Scripts\rayoptics-script.py", line 9, in <module>
    sys.exit(main())
  File "C:\Users\users\Anaconda3\envs\rayoptics\lib\site-packages\rayoptics\qtgui\rayopticsapp.py", line 563, in main
    logging.basicConfig(filename='rayoptics.log',
  File "C:\Users\users\Anaconda3\envs\rayoptics\lib\logging\__init__.py", line 2003, in basicConfig
    h = FileHandler(filename, mode,
  File "C:\Users\users\Anaconda3\envs\rayoptics\lib\logging\__init__.py", line 1146, in __init__
    StreamHandler.__init__(self, self._open())
  File "C:\Users\users\Anaconda3\envs\rayoptics\lib\logging\__init__.py", line 1175, in _open
    return open(self.baseFilename, self.mode, encoding=self.encoding,
PermissionError: [Errno 13] Permission denied: 'C:\\Users\\rayoptics.log'

Handling this as an exception in line 563 of rayopticsapp.py might be a possible fix:

def main():
    try:
        logging.basicConfig(filename='rayoptics.log',
                            filemode='w',
                            level=logging.INFO)
    except:
        logging.basicConfig(filename=Path.home().joinpath('rayoptics.log'),
                            filemode='w',
                            level=logging.INFO)

Since different operating systems use different directories for log files, I find it difficult to find a good cross-platform solution.