Release v4.0.0

• Structural rewrite of the internal workings of the library that utilizes CommandRunner, Command and FlagCommand
  classes for better overall structure.
• Renamed info command to about.
• Refactored check-updates flag to check-for-updates.
• Added --license flag command.
• Added --docs flag command.
• create command no longer checks for current directory to be a Flutter project.
• Fixes existing config detection for --add-in-pubspec flag in create command.
• Fixes stacktrace logging on error or exception.
• Color-codes success and error messages for better visual differentiation.