replaced deprecated atomic initializer with const fn `new`
re: https://doc.rust-lang.org/std/sync/atomic/constant.ATOMIC_USIZE_INIT.html
the atomic _INIT
constants were deprecated and no longer compile (rustc 1.37.0-nightly (5eeb567a2 2019-06-06)).
use new
instead.
Edited by Ian P. Cooke