API documentation needs a custom theme

We should see try to theme haddock to make the API documentation less busy. Things like instances should be removed. The page structure should be re-organized to remove references to modules (like Prelude). Confusing notation should be removed for fixity declarations (or the entire fixity removed if it can't be phrased in a more friendly way.)

Begin by locating how Haddock currently generates the API documentation and reviewing the treatment of instances, module references such as Prelude, and fixity declarations. Done means a less busy custom theme with clearer page structure, no unnecessary instance or module references, and friendlier fixity notation where it is retained.

Written by the indexing model from the issue text.