[Feature Request] How about nonzero version of ::capacity method?

[tmvkrpxl0]

I'm using nonempty crate for managing vulkan buffers. They can't be zero sized, so nonempty is quite useful. I'm using NonEmpty's capacity as a size of new buffer. I currently just use NonZeroU64::new(nonempty.capacity() as usize).unwrap(). It would be convenient if it just returned NonZeroUSize itself.

[FintanH]

Thanks for the suggestion! This has been resolved in #70