Add native longs KLL sketch

[ZacBlanco]

Our use case would benefit from an implementation for this native type. I considered a commit to refactor some common logic, but found little benefit, so opted to essentially sed s/float/long/ the KllFloatsSketch implementation along with all of the associated classes and tests.

[leerho]

I haven't had a chance to review this carefully, but I will. In principle I am in favor of this.

[jmalkin]

It's not an elegant solution, but effectively doing s/float/long/g is, sadly, a fairly reasonable approach in Java.

[leerho]

Merge into branch "kll_longs_sketch"