Example for vspan and hspan

[tpgillam]

Closes #4051.

Provide example of using vspan and hspan.

[tpgillam]

Looks like I would need to add a new image to https://github.com/JuliaPlots/PlotReferenceImages.jl — what's the usual workflow for doing a PR like this? I'm happy to make a PR there now if we're happy with the example, which generates the following:

[t-bltg]

what's the usual workflow for doing a PR like this?

https://docs.juliaplots.org/latest/contributing/#VisualRegressionTests

[tpgillam]

I've opened a PR on PlotReferenceImages.jl — but that PR will obviously need tweaking if anyone would like the example tweaked :)

[t-bltg]

Looks good.
Please format your pr using $ julia -e 'using JuliaFormatter; format(["src", "test"])' in your Plots.jl fork.

[BeastyBlacksmith]

Also as a first time contributor check out #3503 and consider adding your information to our .zenodo.json file

[codecov]

Codecov Report

Merging #4062 (bca0eb9) into master (311831c) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4062      +/-   ##
==========================================
+ Coverage   62.14%   62.16%   +0.01%     
==========================================
  Files          29       29              
  Lines        7288     7289       +1     
==========================================
+ Hits         4529     4531       +2     
+ Misses       2759     2758       -1     

Impacted Files	Coverage Δ
src/examples.jl	61.76% <ø> (ø)
src/recipes.jl	58.49% <0.00%> (-0.12%)	⬇️
src/backends/gr.jl	88.27% <0.00%> (-0.09%)	⬇️
src/utils.jl	49.92% <0.00%> (+0.15%)	⬆️
src/pipeline.jl	94.24% <0.00%> (+0.47%)	⬆️
src/types.jl	52.17% <0.00%> (+4.34%)	⬆️

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