nn_ins_item factored out of nn_binproc and nn_cinproc

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
nn_ins_item_init and nn_ins_item_term added

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
bind and connect functions moved to nn_ins

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>