def get_orderbook(self, crypto, fiat):
raise NotImplementedError(<EOL>self.name + "<STR_LIT>"<EOL>"<STR_LIT>"<EOL>)<EOL>
Only for exchznges. Returns the current orderbook as a dict with two keys:
bids and asks. Each is a list of floats. The first float is price, the
second is order size.