Expose more structured decoding operations from cborg

[michaelpj]

Codec.CBOR.Term implements encoding/decoding of lists and maps, but they're not exported, so they can't be used elsewhere. For example, the instance for Serialise [a] uses very similar code.

It would be nice to export something like:

decodeListOf :: Decoder s x -> Decoder s [x]
decodeListOf decoder = CBOR.decodeListLenOrIndef >>= \case
  Nothing -> decodeSequenceLenIndef (flip (:)) [] reverse   decoder
  Just n  -> decodeSequenceLenN     (flip (:)) [] reverse n decoder

plus encoding, and maybe something similar for maps?

[michaelpj]

Also perhaps similar things for indefinite-length bytestrings, like the encode/decodeChunked helpers in serialise.