code: def gauge(name, callable = nil, &block)
        add_or_get(name, Metriks::Gauge) do
          Metriks::Gauge.new(callable, &block)
        end
      end
docs: Public: Fetch or create a new gauge metric.
  
   name - The String name of the metric to define or fetch
  
   Examples
  
     registry.gauge('disk_space.used') { 1 }
  
   Returns the Metriks::Gauge identified by the name.