fix: support verbatim code-block with syntax specified (#18)

This is useful for renderes that display syntax highlighting based on
the type. e.g. see:

https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-and-highlighting-code-blocks#syntax-highlighting

main.go

@@ -304,12 +304,12 @@ func readFile(filename string) (e Entry) {
 		}
 
 		trimmedText := strings.TrimSpace(sc.Text())
-		if !verbatim && trimmedText == "```" {
+		if !verbatim && strings.HasPrefix(trimmedText, "```") {
 			// start new paragraph
 			if sect != "" {
 				text = append(text, sect)
 			}
-			sect = "```"
+			sect = trimmedText
 			verbatim = true
 			continue
 		}

main_test.go

@@ -91,13 +91,16 @@ https://github.com/restic/restic/pull/666666
 		{
 			`Enhancement: foo bar subject
 
+` + "```bash\necho 'test code block with type'\n```" + `
+
 https://github.com/restic/restic/issues/12345
 https://github.com/restic/rest-server/issues/232323
 https://github.com/restic/restic/pull/666666
 https://forum.restic.net/t/getting-last-successful-backup-time/531
 `,
 			Entry{
 				Title:      "Foo bar subject",
+				Paragraphs: []string{"```bash\necho 'test code block with type'\n```"},
 				Type:       "Enhancement",
 				TypeShort:  "Enh",
 				PrimaryID:  12345,