Add plugin for SnoopPrecompile.jl

[nickrobinson251]

We could set up the package to have code like

module MyPkg

using SnoopPrecompile

# Write your package code here.

@precompile_setup begin
    # Put here any variables that you want to use in `@precompile_all_calls`
    @precompile_all_calls begin
        # Put here all calls that you want to precompile
    end
end

end

c.f. https://github.com/timholy/SnoopCompile.jl/blob/ad792afcb320971231128479cff9baa3bd1245d0/docs/src/snoop_pc.md

Plus with SnoopPrecompile.jl added to the Project.toml.

Potentially such a plugin could allow users to configure some things e.g. compat for SnoopPrecompile.jl.

[gdalle]

Now called https://github.com/JuliaLang/PrecompileTools.jl