explicit tags for all(?) features

[y-ack]

• \b (bold)
• \u (underline)
• \i (italic)
• \s (strikethrough)
• \quote
• \code
• \icode
• \link (allows naming without bare link?)
• \embed
• \img (same as \embed)
• \hr
• \h1-4 (block)
  i think table tags would just be too [spoiler text] up and don't bother