addendum: if you're like 'when could you want this?', imagine you are deserializing from a Reader which has an internal circular buffer or something from the ne

addendum: if you're like 'when could you want this?', imagine you are deserializing from a Reader which has an internal circular buffer or something from the network (bounded) and you want to limit a peers total resident memory (or something) on your server. Very difficult to do this with Serde!