elliptics: Added size and offset support

Currently for get and upload handlers only
elliptics: Added Ranges request support
elliptics: Added redirect & signature support
elliptics: Removed name from signature
Added http_response::reason
Added read-flow
Merge branch 'master' of github.com:reverbrain/swarm into new-api

Conflicts:
	example/elliptics/io.hpp
Added on_buffered_upload handler