Table of contents improvements

It is now easier to navigate and restructure long docs. Insert a table of contents and it will now stick with you as you read, and you can even reorder your doc directly from it.

• Scroll past a table of contents and it sticks to the left of the page, if there’s room.
• Drag an item in the table of contents to move that section to a new position.

To try it out, click + in a doc (or press the / key) and add a Table of Contents.