Re-add len() and clear() as inherent Headers methods.
Re-add len() and clear() as inherent Headers methods.

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