Add Unicode Histogram functionality

[karajan9]

Example usage:

d = CSV.read(datadir("exp_raw/Howell_1.csv"), copycols = true)
for col in eachcol(d)
    println(unicode_histogram(col))
end

gives

▁▁▁▂▂▂▂▂▂██▆▁
▁▃▄▄▃▂▃▆██▅▃▁
█▆▆▆▆▃▃▁▁
█▁▁▁▁▁▁▁▁▁█

I'm not sure how to incorporate this with precis since it would probably turn the array type in to a Union. Unicode and font coverage is also necessary but that seems to be pretty good in the Julia community (heavy Unicode symbol usage, strings are UTF-8...).

[karajan9]

To show where the histogram is coming from since almost everything is missing from the Unicode one:

f = fit(Histogram, d.weight, nbins = 12)
plot(f)
hline!(range(0, maximum(f.weights), length = 9))

turns into ▁▃▄▄▃▂▃▆██▅▃▁

I'm not quite happy with how the Unicode is displayed in my browser, apparently that font isn't as nice, so results my vary.

[goedman]

This looks great! Definitely would be great if we can indeed integrate into precis(), I'll have a look.

Precis in my mind is kind of a "quick peek" at the results, maybe quality of display is slightly less important. In many of the examples in the book I didn't always find the histograms convincing.

When experimenting with UnicodePlots I did run into the issue of dispatch conflicts with StatsPlots. We will have to decide if we always want users to fully qualify method names. I might have to clean that up for plotcoef, plotbounds, etc. when Unicode histograms become part of precis.

[karajan9]

maybe quality of display is slightly less important

Right, I see it as only differentiating between maybe uniform, symmetric, asymmetric, (categorical?), and "weird". Fine for the very first overview but for anything else something else is needed.

When experimenting with UnicodePlots

I'm not sure if we are misunderstanding each other here, the histogram uses Unicode symbols to show the bars but isn't built on UnicodePlots. The method as it is right now shouldn't cause any conflicts (maybe with fit? But since that's not in user code it's easy for us to fix to StatsBase.fit).

[goedman]

Aah, I see, very neat! Will try to incorporate it in the display of precis().