v0.20.0+reedsy.1

• Merges PR slab#404 (Add methods for retrieving formats applied to a range.)
• Merges PR slab#430 (Headings)
• Add support for Blockquote ('quote' format)
• Change default block tag from <div> to <p>
• Merges PR slab#438 (Add superscript and subscript support)