Log21

Fixed import error in tkinter-less environments.

Minor changes.

Added optional shell support to the LoggingWindow.

Added LoggingWindow!

Minor changes.

Added `ProgressBar` class!

You can directly print a progress bar to the console using `print_progress` method of `log21.Logger` class.

OR

Use `log21.ProgressBar` class witch is specifically designed for this purpose.

OR

Use `log21.progress_bar` function (I don't recommend it!).