Add `out` parameter to ReductionKernel call.
Merge pull request #51 from gw0/add-reduction-out-with-offset

Add `out` parameter to ReductionKernel call.
Add change remark about out parameter in ReductionKernel
Merge branch 'master' into cffi
pyopencl_call_guarded
error
pyopencl_call_guarded_cleanup
pyopencl_buf
cast_bool
get_vec_info
get_opaque_info
get_str_info
get_int_info
noncopyable
c_handle_error
convert_obj
python gc
clean up
from_class/to_class
clean up