Enable more hints for HLint.

[chungyc]

The specific hints that are enabled are Fuse foldr/map, Use :, Use camelCase, Use concatMap, Use maybe, Use newtype instead of data, and Use replicate.

These are the last of the hints I will be enabling, which seem uncontroversial enough. The rest range from those that I am ambivalent about (e.g., Eta reduce; point-free style is fine, but I don't feel that we need to strive to be point-free as much as possible) to those I think are a bad idea (e.g., Use <$; it's a generally obscure enough operator that isn't used enough in this code base for it to become naturally familiar with).

[blackgnezdo]

I agree that all the enabled warnings are uncontroversial. Thanks for all these cleanups!