Make MUNGE generated table of contents (TOC) bookmark work when there are symbols in the headline

cmd/mungedocs/toc_test.go

@@ -37,6 +37,10 @@ func Test_buildTOC(t *testing.T) {
 			"# Title\nLorem ipsum \n## Section Heading\ndolor sit amet\n```bash\n#!/bin/sh\n```",
 			"- [Title](#title)\n  - [Section Heading](#section-heading)\n",
 		},
+		{
+			"# Title\nLorem ipsum \n## Section Heading\n### Why doesn't this work?\ndolor sit amet\n",
+			"- [Title](#title)\n  - [Section Heading](#section-heading)\n    - [Why doesn't this work?](#why-doesnt-this-work)\n",
+		},
 	}
 	for _, c := range cases {
 		actual, err := buildTOC([]byte(c.in))