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, 0 insertions, 27 deletions

diff --git a/helpers/general.go b/helpers/general.go
index 80c0591b2..259bcf8f4 100644
--- a/helpers/general.go
+++ b/helpers/general.go
@@ -44,11 +44,6 @@ import (
 // FilePathSeparator as defined by os.Separator.
 const FilePathSeparator = string(filepath.Separator)
 
-// Strips carriage returns from third-party / external processes (useful for Windows)
-func normalizeExternalHelperLineFeeds(content []byte) []byte {
-	return bytes.Replace(content, []byte("\r"), []byte(""), -1)
-}
-
 // FindAvailablePort returns an available and valid TCP port.
 func FindAvailablePort() (*net.TCPAddr, error) {
 	l, err := net.Listen("tcp", ":0")
@@ -74,28 +69,6 @@ func InStringArray(arr []string, el string) bool {
 	return false
 }
 
-// GuessType attempts to guess the type of file from a given string.
-func GuessType(in string) string {
-	switch strings.ToLower(in) {
-	case "md", "markdown", "mdown":
-		return "markdown"
-	case "asciidoc", "adoc", "ad":
-		return "asciidoc"
-	case "mmark":
-		return "mmark"
-	case "rst":
-		return "rst"
-	case "pandoc", "pdc":
-		return "pandoc"
-	case "html", "htm":
-		return "html"
-	case "org":
-		return "org"
-	}
-
-	return ""
-}
-
 // FirstUpper returns a string with the first character as upper case.
 func FirstUpper(s string) string {
 	if s == "" {