def consume_item(rlp, start):
p, t, l, s = consume_length_prefix(rlp, start)<EOL>return consume_payload(rlp, p, s, t, l)<EOL>
Read an item from an RLP string.

    :param rlp: the rlp string to read from
    :param start: the position at which to start reading
    :returns: a tuple ``(item, per_item_rlp, end)``, where ``item`` is
              the read item, per_item_rlp is a list containing the RLP
              encoding of each item and ``end`` is the position of the
              first unprocessed byte