BREAKING CHANGE: Command.option no longer accepts individual arguments, an object must be passed.

BREAKING CHANGE: Command.variable no longer accepts individual arguments, an object must be passed.

BREAKING CHANGE: Command.parameter no longer accepts individual arguments, an object must be passed.

BREAKING CHANGE: Arguments and options are now members of the context object, and not passed to handlers directly.

BREAKING CHANGE: The 'multiple' option is now called 'variadic'.

BREAKING CHANGE: The 'global' option is now called 'inherit', and must be specified in an options object.

BREAKING CHANGE: The error message for Context.fatal and Context.usage is no longer optional.
BREAKING CHANGE: The exit code for Context.fatal and Context.usage is now the first argument.

BREAKING CHANGE: Command.log and Context.log no longer exist.

BREAKING CHANGE: Context.name and Context.path are now strings rather than functions.