deserialize into allocator

[MarcWeber]

I read that Rust nightly introduces allocators. There are some arena allocators like bumpalo. So eventually decode should be passed an allocator ? In my case I read millions of [u8] into bumpalo. Not important for me to fix it right now.

[adamreichold]

I think that instead of special casing allocators, there should be something like Serde's DeserializeSeed for stateful decoding where the state could for example be an allocator.

[VictorKoenders]

There's #710 which might help with this