3.0.0

• fa392c2 Add spread to List, ListItem (see remarkjs/remark#364)
• dbb1ede Add label to Association (see GH-23)
• f49890b Rewrite specification (see syntax-tree/unist#17, syntax-tree/unist#18, GH-21, GH-24)
• 5bf6788 Change info in Code to meta (see GH-22)
• d797ea3 Add info to Code (see GH-22)