Added link to content page

[tkburis]

I'm working through the book, and I'm finding it a bit awkward to navigate back to the contents page. So I have added a link to contents from the floating navbars.

This looks fine when the navbar is stretched. However, on some pages, or when you scroll down, it squashes, which doesn't look as good. Maybe someone who knows the project better than me can improve on this?

   This looks fine, IMO.

   Scrolling down... not quite as nice?

   The final page also doesn't look quite right.