chmop($x) should suggest chomp

I didn't realize I was mashing together two conceptually independent commits. I am not sure how to disentangle everything right now. If this is too disorganized, feel free to reject this request, and I will fix things.

This overlaps with my previous request regarding using an exception object. I did a little clean up of that.

But the more important part concerns the matching algorithm used. `Text::Levenshtein` does not take into account transpositions which results in `chomp` not being suggested when `chmop($x)` is encountered.

I tried to fix that by using `Text::Levenshtein::Damerau::XS`. Seems to work in that particular case.