Reuse the BlackFriday instance when possible

This is in heavy use in rendering, so this makes a difference:

```bash
benchmark                                                                                    old ns/op     new ns/op     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_pages=500,tags_per_page=5,shortcodes,render-4     124551144     107743429     -13.49%

benchmark                                                                                    old allocs     new allocs     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_pages=500,tags_per_page=5,shortcodes,render-4     528684         435118         -17.70%

benchmark                                                                                    old bytes     new bytes     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_pages=500,tags_per_page=5,shortcodes,render-4     53306848      45147832      -15.31%
```

1 files changed, 11 insertions, 11 deletions

diff --git a/helpers/content_test.go b/helpers/content_test.go
index 8f2d44cd9..c10ad881b 100644
--- a/helpers/content_test.go
+++ b/helpers/content_test.go
@@ -159,7 +159,7 @@ func TestTruncateWordsByRune(t *testing.T) {
 
 func TestGetHTMLRendererFlags(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	renderer := c.getHTMLRenderer(blackfriday.HTML_USE_XHTML, ctx)
 	flags := renderer.GetFlags()
 	if flags&blackfriday.HTML_USE_XHTML != blackfriday.HTML_USE_XHTML {
@@ -186,7 +186,7 @@ func TestGetHTMLRendererAllFlags(t *testing.T) {
 		{blackfriday.HTML_SMARTYPANTS_LATEX_DASHES},
 	}
 	defaultFlags := blackfriday.HTML_USE_XHTML
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Config.AngledQuotes = true
 	ctx.Config.Fractions = true
 	ctx.Config.HrefTargetBlank = true
@@ -209,7 +209,7 @@ func TestGetHTMLRendererAllFlags(t *testing.T) {
 
 func TestGetHTMLRendererAnchors(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.DocumentID = "testid"
 	ctx.Config.PlainIDAnchors = false
 
@@ -233,7 +233,7 @@ func TestGetHTMLRendererAnchors(t *testing.T) {
 
 func TestGetMmarkHTMLRenderer(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.DocumentID = "testid"
 	ctx.Config.PlainIDAnchors = false
 	actualRenderer := c.getMmarkHTMLRenderer(0, ctx)
@@ -257,7 +257,7 @@ func TestGetMmarkHTMLRenderer(t *testing.T) {
 
 func TestGetMarkdownExtensionsMasksAreRemovedFromExtensions(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"headerId"}
 	ctx.Config.ExtensionsMask = []string{"noIntraEmphasis"}
 
@@ -272,7 +272,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 		testFlag int
 	}
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{""}
 	ctx.Config.ExtensionsMask = []string{""}
 	allExtensions := []data{
@@ -304,7 +304,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 
 func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"definitionLists"}
 	ctx.Config.ExtensionsMask = []string{""}
 
@@ -316,7 +316,7 @@ func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
 
 func TestGetMarkdownRenderer(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.markdownRender(ctx)
 	expectedRenderedMarkdown := []byte("<p>testContent</p>\n")
@@ -327,7 +327,7 @@ func TestGetMarkdownRenderer(t *testing.T) {
 
 func TestGetMarkdownRendererWithTOC(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{RenderTOC: true, Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{RenderTOC: true, Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.markdownRender(ctx)
 	expectedRenderedMarkdown := []byte("<nav>\n</nav>\n\n<p>testContent</p>\n")
@@ -342,7 +342,7 @@ func TestGetMmarkExtensions(t *testing.T) {
 		testFlag int
 	}
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"tables"}
 	ctx.Config.ExtensionsMask = []string{""}
 	allExtensions := []data{
@@ -371,7 +371,7 @@ func TestGetMmarkExtensions(t *testing.T) {
 
 func TestMmarkRender(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.NewBlackfriday()}
+	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.mmarkRender(ctx)
 	expectedRenderedMarkdown := []byte("<p>testContent</p>\n")