Add document: block html, span html.

Signed-off-by: CyberZHG <CyberZHG@gmail.com>
Add line number area to editor.

Signed-off-by: CyberZHG <CyberZHG@gmail.com>
Use MarkdownEditor instead of Editor.

Signed-off-by: cyberzhg <cyberzhg@gmail.com>