module XSemVer::DSL::InstanceMethods

def run_command(command)

Raises CommandError if the command does not exist.
Calls an instance method defined via the ::command class method. 
def run_command(command)
  method_name = "#{self.class.command_prefix}#{command}"
  if self.class.method_defined?(method_name)
    send method_name
  else
    raise CommandError, "invalid command #{command}"
  end
end