Remove unnecessary type alias for strings.Builder

TIL embedded types can be acessed by their non-namespaced name - so there
actually is no need for a type alias to access .strings.Builder, one can just
use .Builder.

org/html_writer.go

@@ -14,7 +14,7 @@ import (
 
 // HTMLWriter exports an org document into a html document.
 type HTMLWriter struct {
-	stringBuilder
+	strings.Builder
 	document           *Document
 	HighlightCodeBlock func(source, lang string) string
 	htmlEscape         bool
@@ -57,7 +57,7 @@ func NewHTMLWriter() *HTMLWriter {
 
 func (w *HTMLWriter) emptyClone() *HTMLWriter {
 	wcopy := *w
-	wcopy.stringBuilder = stringBuilder{}
+	wcopy.Builder = strings.Builder{}
 	return &wcopy
 }
 

org/org_writer.go

@@ -7,12 +7,10 @@ import (
 	"unicode/utf8"
 )
 
-type stringBuilder = strings.Builder
-
 // OrgWriter export an org document into pretty printed org document.
 type OrgWriter struct {
 	TagsColumn int
-	stringBuilder
+	strings.Builder
 	indent string
 }
 
@@ -38,7 +36,7 @@ func (w *OrgWriter) After(d *Document)  {}
 
 func (w *OrgWriter) emptyClone() *OrgWriter {
 	wcopy := *w
-	wcopy.stringBuilder = strings.Builder{}
+	wcopy.Builder = strings.Builder{}
 	return &wcopy
 }