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/low/v3/encoding_test.go

@@ -0,0 +1,64 @@
+// Copyright 2022 Princess B33f Heavy Industries / Dave Shanley
+// SPDX-License-Identifier: MIT
+
+package v3
+
+import (
+	"github.com/pb33f/libopenapi/datamodel/low"
+	"github.com/pb33f/libopenapi/index"
+	"github.com/stretchr/testify/assert"
+	"gopkg.in/yaml.v3"
+	"testing"
+)
+
+func TestEncoding_Build_Success(t *testing.T) {
+
+	yml := `contentType: hot/cakes
+headers: 
+  ohMyStars:
+    description: this is a header
+    required: true
+    allowEmptyValue: true
+allowReserved: true    
+explode: true`
+
+	var idxNode yaml.Node
+	mErr := yaml.Unmarshal([]byte(yml), &idxNode)
+	assert.NoError(t, mErr)
+	idx := index.NewSpecIndex(&idxNode)
+
+	var n Encoding
+	err := low.BuildModel(&idxNode, &n)
+	assert.NoError(t, err)
+
+	err = n.Build(idxNode.Content[0], idx)
+	assert.NoError(t, err)
+	assert.Equal(t, "hot/cakes", n.ContentType.Value)
+	assert.Equal(t, true, n.AllowReserved.Value)
+	assert.Equal(t, true, n.Explode.Value)
+
+	header := n.FindHeader("ohMyStars")
+	assert.NotNil(t, header.Value)
+	assert.Equal(t, "this is a header", header.Value.Description.Value)
+	assert.Equal(t, true, header.Value.Required.Value)
+	assert.Equal(t, true, header.Value.AllowEmptyValue.Value)
+}
+
+func TestEncoding_Build_Error(t *testing.T) {
+
+	yml := `contentType: hot/cakes
+headers: 
+  $ref: #/borked`
+
+	var idxNode yaml.Node
+	mErr := yaml.Unmarshal([]byte(yml), &idxNode)
+	assert.NoError(t, mErr)
+	idx := index.NewSpecIndex(&idxNode)
+
+	var n Encoding
+	err := low.BuildModel(&idxNode, &n)
+	assert.NoError(t, err)
+
+	err = n.Build(idxNode.Content[0], idx)
+	assert.Error(t, err)
+}