Add a get_raw method, which allows users to access the raw value of a header
Add a get_raw method, which allows users to access the raw value of a header

This method is marked unsafe, as it should not be used in normal code
because it can easily invalidate header representations.

Fixes #10

mlalic/hyper,markuskobler/hyper,Twey/hyper,Twey/hyper,steveklabnik/hyper,fhahn/hyper,ianks/hyper,pyfisch/hyper,Twey/hyper,mlalic/hyper,yazaddaruvala/hyper,yazaddaruvala/hyper,hyperium/hyper,mikedilger/hyper,Keats/hyper,peterhj/hyper,nstoddard/hyper,bonifaido/hyper,mre/hyper,pcwalton/hyper,Manishearth/hyper,lame-nickname/hyper,yangxingpping/hyper,bheesham/hyper,tshepang/hyper,fuchsnj/hyper,sfackler/hyper,PeterReid/hyper,tempbottle/hyper,manuel-woelker/hyper,nstoddard/hyper,rschulman/hyper,nickgonzales/hyper,achanda/hyper,Ryman/hyper,erickt/hyper,mfeckie/hyper,Keats/hyper,golddranks/hyper,hyperium/hyper,softprops/hyper,tshepang/hyper,reem/hyper,TimNN/hyper,huonw/hyper,mneumann/hyper,hannobraun/hyper,golddranks/hyper,servo/hyper,frewsxcv/hyper,giftcards/hyper,clatour/hyper,hannobraun/hyper,Keats/hyper,markuskobler/hyper,fengsp/hyper,markuskobler/hyper,hannobraun/hyper,retep998/hyper,jmmaranan/hyper,youprofit/hyper,golddranks/hyper,hyperium/hyper,nickgonzales/hyper,nickgonzales/hyper,mitsuhiko/hyper,tshepang/hyper