Initial CRAN release

This release contains the most of the basic markdown functionality described in the GFM spec:

4 Leaf blocks

• 4.1 Thematic breaks = md_break()
• 4.2 ATX headings = md_heading()
• 4.3 Setext headings = md_setext()
• 4.4 Indented code blocks = md_indent()
• 4.5 Fenced code blocks = md_fence()
• 4.6 HTML blocks = md_convert()
• 4.7 Link reference definitions = md_reference()
• 4.8 Paragraphs = md_paragraph()
• 4.9 Blank lines = md_blank()
• 4.10 Tables (extension) = md_table()

5 Container blocks

• 5.1 Block quotes = md_quote()
• 5.3 Task list items (extension) = md_task()
• 5.4 Lists = md_list() (todo: indented sub-lists)
  • md_order()
  • md_bullet()

6 Inlines

• 6.1 Backslash escapes = md_escape()
• 6.3 Code spans = md_code()
• 6.4 Emphasis = md_italic()
• 6.4 Strong emphasis = md_bold()
• 6.5 Strikethrough (extension) = md_strike()
• 6.6 Links = md_link()
• 6.7 Images = md_image()
• 6.8 Autolinks = md_autolink()
• 6.10 Raw HTML = md_convert()
• 6.11 Disallowed Raw HTML (extension) = md_disallow()
• 6.12 Hard line breaks = md_hardline()
• 6.13 Soft line breaks = md_softline()
• 6.14 Textual content = md_text()