MD text renderer: handle backslashes

Handles the same characters as the html renderer.

src/parsing/renderer.go

@@ -2,6 +2,7 @@ package parsing
 
 import (
 	"io"
+	"regexp"
 
 	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/renderer"
@@ -11,6 +12,8 @@ type plaintextRenderer struct{}
 
 var _ renderer.Renderer = plaintextRenderer{}
 
+var backslashRegex = regexp.MustCompile("\\\\(?P<char>[\\\\\\x60!\"#$%&'()*+,-./:;<=>?@\\[\\]^_{|}~])")
+
 func (r plaintextRenderer) Render(w io.Writer, source []byte, n ast.Node) error {
 	return ast.Walk(n, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
 		if !entering {
@@ -20,8 +23,7 @@ func (r plaintextRenderer) Render(w io.Writer, source []byte, n ast.Node) error
 		switch n.Kind() {
 		case ast.KindText:
 			n := n.(*ast.Text)
-
-			_, err := w.Write(n.Text(source))
+			_, err := w.Write(backslashRegex.ReplaceAll(n.Text(source), []byte("$1")))
 			if err != nil {
 				return ast.WalkContinue, err
 			}