Lack of support for vmaCopyMemoryToAllocation

[tuxerr]

Hey!
I see vmaCopyMemoryToAllocation in ffi.rs:

    pub fn vmaCopyMemoryToAllocation(

but not used at all in lib.rs and I can't find a way to use it in my program. This might be me being new at Rust, but if not is there a reason for the lack of support, and if not would you accept a PR to have it as a method on vk_mem::Allocator?

Thanks for the excellent lib. :)