mcorrell

`mode` is a little tricky, and I think the current datalib `map` function might be more useful in 99% of cases. For instance, `mode([1,2])` should, in principle, return the unordered...

Okay, I made a PR #91 that adds sample skew. I wasn't sure how to sunset `modeskew` exactly so I just punted on that.

From #5 we now have "us" (which _de-_saturates colors as uncertainty increases) and "ul" (which lightens colors as uncertainty increases).