Adding bandlines functions/block ?

[gybefloyd]

Hi, thanks for the very nice package.
I usually plot error bars as band plots with the mean curve on top.
In the same spirit as scatterlines it would be nice to have a single function plotting a Line and a Band altogether giving a single entry in the legend.
I'm using this kind of function for instance:

function bandlines!(f,x,y,yerr; color=blue, linewidth=1.0, bandcolor=(blue,0.15), label=nothing)
    y_lo = y.(x) - 1.96*yerr.(x)
    y_hi = y.(x) + 1.96*yerr.(x)
    band = band!(f, x, y_lo, y_hi, color=bandcolor, label=label);
    lines = lines!(f, x, y; linewidth=linewidth, color=color, label=label);
    return band, lines
end

Of course someting more generic as bandlines!(f,x,y,y_lo,y_hi; kwargs...) would be much better.

Also, why not passing functions and not just vectors to band to specify the upper and lower bounds ?

Best,
Amaël