This crate provides a [Cell] type (like the standard library’s
Cell) with methods for safely mutating and inspecting the
inner value by reference ([with] and [with_mut]).
For [Copy] types, this is implemented with get and
set, but through an extension trait, this crate
provides those same operations for types that are [Default] but not
[Copy]. A [get] method is also available for types that are both
[Default] and [Clone].