Add Goldmark as the new default markdown handler

This commit adds the fast and CommonMark compliant Goldmark as the new default markdown handler in Hugo.

If you want to continue using BlackFriday as the default for md/markdown extensions, you can use this configuration:

```toml
[markup]
defaultMarkdownHandler="blackfriday"
```

Fixes #5963
Fixes #1778
Fixes #6355

1 files changed, 19 insertions, 10 deletions

diff --git a/hugolib/hugo_sites_build_test.go b/hugolib/hugo_sites_build_test.go
index 1a690cdd9..03853bff6 100644
--- a/hugolib/hugo_sites_build_test.go
+++ b/hugolib/hugo_sites_build_test.go
@@ -671,7 +671,7 @@ END
 
 	b.CreateSites().Build(BuildCfg{})
 
-	contentMatchers := []string{"<h2 id=\"another-header\">Another header</h2>", "<h2 id=\"another-header-99\">Another header</h2>", "<p>The End.</p>"}
+	contentMatchers := []string{"<h2 id=\"another-header\">Another header</h2>", "<h2 id=\"another-header99\">Another header</h2>", "<p>The End.</p>"}
 
 	for i := 1; i <= numPages; i++ {
 		if i%3 != 0 {
@@ -691,13 +691,13 @@ END
 		checkContent(b, fmt.Sprintf("public/%s/page%d/index.json", section, i), contentMatchers...)
 	}
 
-	checkContent(b, "public/s1/index.html", "P: s1/_index.md\nList: 10|List Content: 8335\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8335\n\nRender 1: View: 8335\n\nRender 2: View: 8335\n\nRender 3: View: 8335\n\nRender 4: View: 8335\n\nEND\n")
-	checkContent(b, "public/s2/index.html", "P: s2/_index.md\nList: 10|List Content: 8335", "Render 4: View: 8335\n\nEND")
-	checkContent(b, "public/index.html", "P: _index.md\nList: 10|List Content: 8335", "4: View: 8335\n\nEND")
+	checkContent(b, "public/s1/index.html", "P: s1/_index.md\nList: 10|List Content: 8033\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8033\n\nRender 1: View: 8033\n\nRender 2: View: 8033\n\nRender 3: View: 8033\n\nRender 4: View: 8033\n\nEND\n")
+	checkContent(b, "public/s2/index.html", "P: s2/_index.md\nList: 10|List Content: 8033", "Render 4: View: 8033\n\nEND")
+	checkContent(b, "public/index.html", "P: _index.md\nList: 10|List Content: 8033", "4: View: 8033\n\nEND")
 
 	// Check paginated pages
 	for i := 2; i <= 9; i++ {
-		checkContent(b, fmt.Sprintf("public/page/%d/index.html", i), fmt.Sprintf("Page: %d", i), "Content: 8335\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8335", "Render 4: View: 8335\n\nEND")
+		checkContent(b, fmt.Sprintf("public/page/%d/index.html", i), fmt.Sprintf("Page: %d", i), "Content: 8033\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8033", "Render 4: View: 8033\n\nEND")
 	}
 }
 
@@ -977,7 +977,10 @@ enableRobotsTXT = true
 [permalinks]
 other = "/somewhere/else/:filename"
 
-[blackfriday]
+# TODO(bep)
+[markup]
+  defaultMarkdownHandler = "blackfriday"
+[markup.blackfriday]
 angledQuotes = true
 
 [Taxonomies]
@@ -1035,7 +1038,10 @@ enableRobotsTXT: true
 permalinks:
     other: "/somewhere/else/:filename"
 
-blackfriday:
+# TODO(bep)
+markup:
+  defaultMarkdownHandler: blackfriday
+  blackFriday:
     angledQuotes: true
 
 Taxonomies:
@@ -1093,9 +1099,12 @@ var multiSiteJSONConfigTemplate = `
   "permalinks": {
     "other": "/somewhere/else/:filename"
   },
-  "blackfriday": {
-    "angledQuotes": true
-  },
+  "markup": {
+		"defaultMarkdownHandler": "blackfriday",
+		"blackfriday": {
+	    "angledQuotes": true
+	  }
+   },
   "Taxonomies": {
     "tag": "tags"
   },