Fix haddocks on infix constructors

[brandonchinn178]

Resolves #758. Recommend reviewing commit-by-commit

[amesgen]

Thanks!

While the refactorings in the first three commits don't seem strictly necessary, they are nicely separated and make sense in the context of the additional where bindings introduced later.

Minor: I usually review changes that involve formatting with difftastic, so I would even be fine if you didn't separate out the formatting commits, but it certainly doesn't hurt; your efforts to increase reviewability are really appreciated!

[brandonchinn178]

I always organize my commits anyway, because it's easier for me to reorganize and edit my own work 😃