Fails with `NotEnough` error in arbitrary parsing functions

[joshtriplett]

As far as I can tell, when cbor_event deserializes from a BufRead instance, it only calls fill_buf when calling get (and then only once), not when calling advance. So, any arbitrary parsing function may potentially return a NotEnough error in the middle of its parsing, requiring any higher-level protocol parsing built atop that to handle any parsing function failing with NotEnough and retry after fetching more data.

[NicolasDP]

Thanks for your contributions and looking into this repo. I'll be looking at them this week.

[SebastienGllmt]

Note: while the premise of the issue no longer applies (v3 removed reader-based input entirely. Deserializer owns a complete Vec<u8> and there is nothing to refill), the library doesn't have a streaming API which is what I think is the core feature ask of this issue

The library instead assumes a "save-position/rewind pattern" and tries to guarantee there won't be a panic on parse failures, and hopefully with the fix to #4 you can do this reliably do position()/set_position() + NotEnough

Unless somebody wants/builds a streaming API, this is the best we can do at the moment