Refactored version directory names

3.0 and 2.0 do not work, there are multiple versions and anything with a period in it sucks from my point of view, v2 and v3 feel much better from a DX perspective.

datamodel/high/v3/server_variable.go

@@ -0,0 +1,32 @@
+// Copyright 2022 Princess B33f Heavy Industries / Dave Shanley
+// SPDX-License-Identifier: MIT
+
+package v3
+
+import low "github.com/pb33f/libopenapi/datamodel/low/v3"
+
+type ServerVariable struct {
+	Enum        []string
+	Default     string
+	Description string
+	low         *low.ServerVariable
+}
+
+func NewServerVariable(variable *low.ServerVariable) *ServerVariable {
+	v := new(ServerVariable)
+	v.low = variable
+	var enums []string
+	for _, enum := range variable.Enum {
+		if enum.Value != "" {
+			enums = append(enums, enum.Value)
+		}
+	}
+	v.Default = variable.Default.Value
+	v.Description = variable.Description.Value
+	v.Enum = enums
+	return v
+}
+
+func (s *ServerVariable) GoLow() *low.ServerVariable {
+	return s.low
+}