make api documentation more user-friendly

[jthornbrue]

I find the plotly API documentation difficult to navigate and use. It would be easier if nested APIs were collapsed by default, or better yet given their own page as first-class citizens. When it gets three or four levels deep, I have a hard time finding what I’m looking for, and it’s almost useless. I always start with one of the demo examples that’s closest to what I want to do, but I usually need to modify it a bit, and it’s difficult to find the right documentation and then navigate it to easily find all the options I want to configure.