
A witness can public a price feed for the HIVE:HBD market. The median price
feed is used to process conversion requests between HBD and HIVE.

Parameters:
    witness: The witness publishing the price feed (type: const string &)
    exchange_rate: The desired exchange rate (type: const
	wallet_serializer_wrapper<price> &)
    broadcast: true if you wish to broadcast the transaction (type: bool)
