Support Custom Allocators

[zhuxiujia]

may be

let mut bits = BitVec::from_bytes(&mut mmap[..]);

but now (can't be mut)

let mut bits = BitVec::from_bytes(&mmap[..]);

[pczarn]

Nope, you'd better use a custom Allocator

This is not so simple and easy, if I understand you right

[pczarn]

If I understand you right, you need stuff like https://docs.rs/outsource-heap/latest/outsource_heap/

Changing the issue name