This differs from MMA, but I don't think the MMA behaviour makes sense.

There are two factors to consider:
* The limit of `ArcCoth[x]` as `x -> 0` does not exist e.g. the two limits along the real line are `± Pi I / 2`.
* `ArcCoth[0]` is defined as `Pi I / 2`

I don't think it makes sense to extend the definition to inexact zeros.