v6.0.0-alpha.2

• Dropped support for Python 2 and Python versions below Python 3.5.
• Added type hints and added mypy to CI (#83).
• Support 256 colour ANSI codes (#88).
• Support "light" ANSI codes (#87).
• Support the NO_COLOR environment variable, and a no_color option (#70).
• Updates various examples and documenation (#85).
• Merged TTYColoredFormatter into ColoredFormatter, and ensure no ANSI codes are printed when colors are disabled.
• Replaced LevelFormatter with a far simpler implementation.
• Fixed version_info check for the Formatter validate parameter.
• Define formatMessage instead of format, so that ColoredRecord is used in fewer places.