Update markdown parsing library to github.com/gomarkdown/markdown (#944)

vendor/github.com/gomarkdown/markdown/html/callouts.go

@@ -0,0 +1,42 @@
+package html
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/gomarkdown/markdown/ast"
+	"github.com/gomarkdown/markdown/parser"
+)
+
+// EscapeHTMLCallouts writes html-escaped d to w. It escapes &, <, > and " characters, *but*
+// expands callouts <<N>> with the callout HTML, i.e. by calling r.callout() with a newly created
+// ast.Callout node.
+func (r *Renderer) EscapeHTMLCallouts(w io.Writer, d []byte) {
+	ld := len(d)
+Parse:
+	for i := 0; i < ld; i++ {
+		for _, comment := range r.opts.Comments {
+			if !bytes.HasPrefix(d[i:], comment) {
+				break
+			}
+
+			lc := len(comment)
+			if i+lc < ld {
+				if id, consumed := parser.IsCallout(d[i+lc:]); consumed > 0 {
+					// We have seen a callout
+					callout := &ast.Callout{ID: id}
+					r.callout(w, callout)
+					i += consumed + lc - 1
+					continue Parse
+				}
+			}
+		}
+
+		escSeq := Escaper[d[i]]
+		if escSeq != nil {
+			w.Write(escSeq)
+		} else {
+			w.Write([]byte{d[i]})
+		}
+	}
+}