Basic Markdown support

[netvl]

Tracking issue for basic Markdown syntax support.

• Paragraphs
  • Single emphasis
  • Double emphasis
  • Inline code blocks
  • Newlines
  • Links
    • Inline links
    • Reference links
    • Shortcut reference links
    • Automatic links
    • Images
• HTML blocks
• Headers
  • ATX headers
  • Setext headers
  • ATX headers right after paragraphs
• Blockquotes
• Indented code blocks
• Fenced code blocks
• Horizontal rules
• Reference links blocks
• Lists
  • Ordered lists
  • Unordered lists