V2 low-base docs in place

refactored constants a little also to clean things up.

datamodel/high/base/example.go

@@ -9,7 +9,7 @@ import (
 	low "github.com/pb33f/libopenapi/datamodel/low/base"
 )
 
-// Example represents an Example object as defined by OpenAPI 3+
+// Example represents a high-level Example object as defined by OpenAPI 3+
 //  v3 - https://spec.openapis.org/oas/v3.1.0#example-object
 type Example struct {
 	Summary       string