perf(body): specialize BufList::copy_to_bytes (#2413)
perf(body): specialize BufList::copy_to_bytes (#2413)

Some implementations of the Buf trait have an optimized version (for
example Bytes) of copy_to_bytes, opportunistically use that one.
tshepang/hyper,hyperium/hyper,hyperium/hyper,tshepang/hyper,hyperium/hyper,tshepang/hyper