Lots of work on styling internals that enables new rounded styles for block selection and blockquote rows. Also refined decoration animations to stay in better sync with text content.

• Improved block quote styling
• Improved block selection styling
• Changed mergeDistance style property to mergable
• Fixed crash on ⌥Return in a line with spaces
• Fixed editor.transaction API to return result of passed closure
• Fixed block selection to show all rows, not just the ends