Knack

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* Add mechanism to deprecate commands, command groups, arguments and argument options.
* Improve help display support for Unicode.

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* expose a callback to let client side perform extra logics (80)
* output: don't skip false value on auto-tabulating (83)

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* ArgumentsContext.ignore() should use hidden options_list (76)
* Consolidate exception handling (66)

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* Performance optimization - Delay import of platform and colorama (47)
* CLIError: Inherit from Exception directly (65)
* Explicitly state which packages to include (so exclude 'tests') (68)

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* Support command level and argument level validators.
* knack.commands.CLICommandsLoader now accepts a command_cls argument so you can provide your own CLICommand class.
* logging: make determine_verbose_level private method.
* Allow overriding of NAMED_ARGUMENTS
* Only pass valid argparse kwargs to argparse.ArgumentParser.add_argument and ignore the rest
* logging: make determine_verbose_level private method
* Remove cli_command, register_cli_argument, register_extra_cli_argument as ways to register commands and arguments.

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* Add more types of command and argument loaders.