Provide Tree and treeValue public aliases (#467)

Provide public aliases for Tree and treeValue to give more                                                       
control when manipulating TOML documents. This is a stop-gap
measure until we redesign the interface in v2.

Fix #466

tomlpub.go

@@ -0,0 +1,71 @@
+package toml
+
+// PubTOMLValue wrapping tomlValue in order to access all properties from outside.
+type PubTOMLValue = tomlValue
+
+func (ptv *PubTOMLValue) Value() interface{} {
+	return ptv.value
+}
+func (ptv *PubTOMLValue) Comment() string {
+	return ptv.comment
+}
+func (ptv *PubTOMLValue) Commented() bool {
+	return ptv.commented
+}
+func (ptv *PubTOMLValue) Multiline() bool {
+	return ptv.multiline
+}
+func (ptv *PubTOMLValue) Position() Position {
+	return ptv.position
+}
+
+func (ptv *PubTOMLValue) SetValue(v interface{}) {
+	ptv.value = v
+}
+func (ptv *PubTOMLValue) SetComment(s string) {
+	ptv.comment = s
+}
+func (ptv *PubTOMLValue) SetCommented(c bool) {
+	ptv.commented = c
+}
+func (ptv *PubTOMLValue) SetMultiline(m bool) {
+	ptv.multiline = m
+}
+func (ptv *PubTOMLValue) SetPosition(p Position) {
+	ptv.position = p
+}
+
+// PubTree wrapping Tree in order to access all properties from outside.
+type PubTree = Tree
+
+func (pt *PubTree) Values() map[string]interface{} {
+	return pt.values
+}
+
+func (pt *PubTree) Comment() string {
+	return pt.comment
+}
+
+func (pt *PubTree) Commented() bool {
+	return pt.commented
+}
+
+func (pt *PubTree) Inline() bool {
+	return pt.inline
+}
+
+func (pt *PubTree) SetValues(v map[string]interface{}) {
+	pt.values = v
+}
+
+func (pt *PubTree) SetComment(c string) {
+	pt.comment = c
+}
+
+func (pt *PubTree) SetCommented(c bool) {
+	pt.commented = c
+}
+
+func (pt *PubTree) SetInline(i bool) {
+	pt.inline = i
+}