Simplify logic of iterutils.chunked
Simplify logic of iterutils.chunked

Rather than building and calculating a new list when setting a limit to
the items returned by `iterutils.chunked`, `itertools.islice` can be
used to reduce the code and take advantage of any optimizations in the
itertools module.

siemens/boltons,zeroSteiner/boltons,suranap/boltons,doublereedkurt/boltons,mgaitan/boltons,kevinastone/boltons,neuropil/boltons,markrwilliams/boltons