Use a better histogram binning algorithm by default

[mjskay]

Sturges is too conservative (usually not enough bins). Possibilities:

• FD will do lots of bins (maybe too many?).
• Scott will generally do more than Sturges and less than FD, where Scott is supposed to be optimal for normal distributions. This makes it an attractive option.
• KernSmooth::dpih is an extension of Scott that should work well on non-normal distributions too. The KernSmooth license is permissive so one option is to look into creating a weighted version of it (we already have weighted versions of the other bin selection algorithms).

[mjskay]

I'd say, Scott for now and if I (or someone else) wanders along and wants to make a weighted variant of KernSmooth::dpi, we'll try that.