Implement proper logging

[iamkroot]

Bug reports would be greatly simplified if there's a proper log file available to the user.

• Probably add a --debug parameter (or --loglevel like ffmpeg), to enable logging debug info too.
• More serious message levels, like anything above debug, should be printed to the screen in addition to being logged to file. Should be easy to implement using log handlers.

Useful links:

1. https://docs.python.org/3/howto/logging.html
2. https://docs.python.org/3/library/logging.html