refactor(header): make Originheader more allocator friendly
refactor(header): make Originheader more allocator friendly

Change the internal representation of Origin to be more allocator
friendly. The internals of the Origin header are now private to allow
changing them in the future.

BREAKING CHANGES:
- Old code that accesses the Origin struct directly will stop working.

Twey/hyper,tshepang/hyper,tshepang/hyper,hyperium/hyper,hyperium/hyper,tshepang/hyper,Twey/hyper,golddranks/hyper,golddranks/hyper,Twey/hyper,golddranks/hyper,hyperium/hyper,nickgonzales/hyper,nickgonzales/hyper,nickgonzales/hyper,yazaddaruvala/hyper,yazaddaruvala/hyper