v2.2.1-beta version

Changelog

Main PRs: #3 #4

• Introduced documentation. (458ca56)
• New Handler.set_level(), Logger.to_group(), Logger.add_handler(), Logger.remove_handler(), Logger.set_level() functions to better control the elements. (c55e8bf)
• Now if you use some_group.subgroup('subgroup', group_color=pyrolog.TextColor.red), then subgroup will use given group_color value, not the parent's group_color. (4c35a4b)
• Added utilities to automatically extend the version. (1b56ecf)
• Added notset log level. (50f233c)
• Presentation example has been updated.
• Many bug fixes.