Transitions in docs

[ceedubs]

I was just looking at http://typelevel.org/cats/typeclasses/applicativetraverse.html (which is really neat!), and it wasn't obvious to me that the series continues with Functor, Applicative, Traverse when I got to the end of the first page. I thought that it was just a work in progress. For these "series"-type docs, it may be good to have a link at the bottom of each page to the next item in the series.

I think it's a bit more obvious for the other sections, but the Applicative and Traversable Functors title is long enough that the text gets wrapped on the table of contents on the left side and threw me off a bit.

[adelbertc]

Related: #1443