Introduce PerlCritic Policy References::ProhibitDoubleSigils

[stefanhaerter]

As discussed today, we agreed on introducing the policy References::ProhibitDoubleSigils into the CodePolicy from rel-11_1 onward (at time of writing referring to CodePolicy branch master).

[stefanhaerter]

Checked violations on rel-11_1 at time of writing. There are 146 violations present.