Expand user-collapsible sections (#699)

[Lysxia]

See #699 for discussion.

[alexbiehl]

Nice, thank you. I think you have to update the tests to make Travis happy.

[hvr]

If I understand this PR correclty, all it does is have example sections expanded by default?

Tbh, we introduced collapsible sections and made them collapsed by default because to hide noisy content (mostly examples) that would clutter haddock pages and make them harder to navigate; so this encodes the "click here for more details" UI-paradigm. If they're expanded by default what's the point of having collapsible sections in the first place? Or put differently, if you have a page with 20 collapsed example sections, you're usually only interested in a single example, so you'd need to expand only a single section of interest. If, however, they were to be expanded by default, you'd have to explicitly go and collapse the other 19 examples you don't care about (but you wouldn't do that anyway; you'd simply not collapse anything, so basically the sensible default is to have everything collapsed, and expand on a by-need basis; the other way round makes little sense IMO as nobody in their right mind is going to manually collapse N-1 sections).

[Lysxia]

@hvr That makes sense. I didn't think this through. I'll think of another way to make these sections more visible...

[ntc2]

@Lysxia I'm excited about your #700 , but this PR seems to do the opposite for examples, and I agree with @hvr that it's a bad idea. However, I think adding a button that toggles visibility of all of the examples (but not the instances) could be useful, while leaving the examples collapsed by default.

[Lysxia]

@ntc2 Thanks! That sounds like a better idea.