Add config option for Blackfriday HTML_HREF_TARGET_BLANK

Fixes #1220

helpers/content.go

@@ -42,6 +42,7 @@ var SummaryDivider = []byte("<!--more-->")
 type Blackfriday struct {
 	AngledQuotes    bool
 	Fractions       bool
+	HrefTargetBlank bool
 	LatexDashes     bool
 	PlainIDAnchors  bool
 	Extensions      []string
@@ -53,6 +54,7 @@ func NewBlackfriday() *Blackfriday {
 	return &Blackfriday{
 		AngledQuotes:    false,
 		Fractions:       true,
+		HrefTargetBlank: false,
 		LatexDashes:     true,
 		PlainIDAnchors:  false,
 	}
@@ -157,6 +159,10 @@ func GetHTMLRenderer(defaultFlags int, ctx *RenderingContext) blackfriday.Render
 		htmlFlags |= blackfriday.HTML_SMARTYPANTS_FRACTIONS
 	}
 
+	if ctx.getConfig().HrefTargetBlank {
+		htmlFlags |= blackfriday.HTML_HREF_TARGET_BLANK
+	}
+
 	if ctx.getConfig().LatexDashes {
 		htmlFlags |= blackfriday.HTML_SMARTYPANTS_LATEX_DASHES
 	}