3.0.0-beta.1

• Restored wrongly removed Command#extend()
• Changed Command's constructor and Command#command(method) to take usage only (i.e. command('name [param]') instead command('name', '[param]'))
• Added Command#clone() method
• Added Command#getCommand(name) and Command#getCommands() methods
• Added Command#getOption(name) and Command#getOptions() methods
• Added Command#messageRef() and Option#messageRef() methods
• Added Command#createOptionValues(values) method
• Added Command#help() method similar to Command#version(), use Command#help(false) to disable default help action option
• Fixed Command#showHelp(), it's now logs help message in console instead of returning it
• Renamed Command#showHelp() into Command#outputHelp()
• Changed Command to store params info (as Command#params) even if no params
• Removed Command#infoOption() method, use action in option's config instead, i.e. option(usage, description, { action: ... })
• Removed Command#infoOptionAction and infoOptionAction option for Command constructor as well
• Removed Command#shortcut() method, use shortcut in option's config instead, i.e. option(usage, description, { shortcut: ... })
• Changed Command#command() to raise an exception when subcommand name already in use
• Removed Command#setOptions() method
• Removed Command#setOption() method
• Removed Command#hasOptions() method
• Removed Command#hasOption() method
• Removed Command#hasCommands() method
• Removed Command#normalize() method (use createOptionValues() instead)
• Changed Option to store params info as Option#params, it always an object even if no params
• Added Option#names() method
• Removed name validation for subcommands
• Allowed a number for options's short name
• Changed argv parse handlers to [init() → applyConfig() → prepareContext()]+ → action()
• Changed exports
  • Added getCommandHelp() function
  • Added Params class
  • Removed Argument class
  • Removed color option