More interesting copulas than gaussian + tests

[lrnv]

hey,

I've replaced the examples with a clayton copula instead of a Gaussian one, in the light of the 2008 crisis. I also added some tests with another copula than the clayton, since your addition allows clearly for such things, it'll be sad to restrict to gaussian dependence structures ;)

[codecov[bot]]

Codecov Report

Merging #41 (d13b0d8) into main (e37c67a) will not change coverage. The diff coverage is n/a.

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@@           Coverage Diff           @@
##             main      #41   +/-   ##
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  Coverage   94.23%   94.23%           
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  Files           4        4           
  Lines         104      104           
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  Hits           98       98           
  Misses          6        6           

Impacted Files	Coverage Δ
src/EconomicScenarioGenerators.jl	96.49% <ø> (ø)

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[alecloudenback]

Thank you very much!