Spider diagrams

[RowanGregoire]

Add spider diagrams to the plotting extension.

[brenhinkeller]

Great! Want to add a quick test along the lines of the one for mapplot in https://github.com/brenhinkeller/StatGeochem.jl/blob/main/test/testExtensions.jl?

[brenhinkeller]

Oh so exporting things from package extensions is weird.. if the function you want to add doesn't already exist in the main package, you have to first export a dummy method from the main package (e.g.

StatGeochem.jl/src/StatGeochem.jl

Lines 48 to 52 in 0bde511

	# Methods exclusively for package extensions
	mapplot() = @warn "`mapplot` requires Plots.jl"
	mapplot!() = @warn "`mapplot!` requires Plots.jl"
	export mapplot, mapplot!

for mapplot), and then import and re-export that in the extension

[RowanGregoire]

Oh I got so close to getting that right