feat(headers): support multiple values for Referrer-Policy header
feat(headers): support multiple values for Referrer-Policy header

Closes #882

Twey/hyper,nickgonzales/hyper,tshepang/hyper,golddranks/hyper,yazaddaruvala/hyper,hyperium/hyper,Keats/hyper,hannobraun/hyper,hannobraun/hyper,markuskobler/hyper,hannobraun/hyper,Keats/hyper,golddranks/hyper,Keats/hyper,markuskobler/hyper,hyperium/hyper,golddranks/hyper,tshepang/hyper,tshepang/hyper,Twey/hyper,markuskobler/hyper,nickgonzales/hyper,Twey/hyper,yazaddaruvala/hyper,nickgonzales/hyper,hyperium/hyper