Implement support for SmallVec<u8; N>?

[bwoods]

…or perhaps a SmallByteBuf<N> wrapper?

[nickray]

Would https://github.com/serde-rs/bytes/pull/18 help?

[bwoods]

The heapless crate is nice, but wouldn't work for my case: almost all of the Vecs being deserialized are under a certain size, but I needed SmallVec’s ability to fall-back to heap allocation for the few special cases.