Implement AddGauge & AddCounter functions

and utilize them in the in the 'system' input plugins.

accumulator.go

@@ -11,6 +11,20 @@ type Accumulator interface {
 		tags map[string]string,
 		t ...time.Time)
 
+	// AddGauge is the same as AddFields, but will add the metric as a "Gauge"
+	// type
+	AddGauge(measurement string,
+		fields map[string]interface{},
+		tags map[string]string,
+		t ...time.Time)
+
+	// AddCounter is the same as AddFields, but will add the metric as a "Counter"
+	// type
+	AddCounter(measurement string,
+		fields map[string]interface{},
+		tags map[string]string,
+		t ...time.Time)
+
 	AddError(err error)
 
 	Debug() bool