Plots.jl: Control colorbar size (and other attributes?)

[ahwillia]

As far as I can tell, there isn't a good way to set the size/scale of the colorbar (see, e.g., https://github.com/stevengj/PyPlot.jl/issues/93)

The following would be nice:

X = randn(100,100)
heatmap(X; colorbar=:left)       # works with some backends already (not pyplot?)
heatmap(X; colorbar=0.5)        # half the default size
heatmap(X; colorbar=[-2,0,2])  # tick marks?

I did a bit of digging to see if I could figure out how to implement the scaling. In PyPlot, you can do the following:

So my original thought was to use the fraction keyword. But, it looks like PyPlot.colorbar(...) isn't called directly by Plots? It looks to me like a new axis with a hard-coded size is created here (am I parsing that correctly?):

https://github.com/tbreloff/Plots.jl/blob/master/src/backends/pyplot.jl#L816

Thanks again for your patient guidance through all of these details Tom.

[mauro3]

It would also be great to have to usual font-selection keywords for colorbar ticklabels and colorbar_title.

[mkborregaard]

See also #302