Utilizing new client and overhauling Accumulator interface

Fixes #280
Fixes #281
Fixes #289

plugins/registry.go

@@ -6,17 +6,15 @@ type Accumulator interface {
 	// Create a point with a value, decorating it with tags
 	// NOTE: tags is expected to be owned by the caller, don't mutate
 	// it after passing to Add.
-	Add(measurement string, value interface{}, tags map[string]string)
-
-	// Create a point with a set of values, decorating it with tags
-	// NOTE: tags and values are expected to be owned by the caller, don't mutate
-	// them after passing to AddFieldsWithTime.
-	AddFieldsWithTime(
-		measurement string,
-		values map[string]interface{},
+	Add(measurement string,
+		value interface{},
 		tags map[string]string,
-		timestamp time.Time,
-	)
+		t ...time.Time)
+
+	AddFields(measurement string,
+		fields map[string]interface{},
+		tags map[string]string,
+		t ...time.Time)
 }
 
 type Plugin interface {