old_contents: from cryptex.exchange.exchange import Exchange
  from cryptex.exchange.cryptsy import Cryptsy
  from cryptex.exchange.btce import BTCE
  
new_contents: from cryptex.exchange.exchange import Exchange
  from cryptex.exchange.cryptsy import Cryptsy, CryptsyPublic
  from cryptex.exchange.btce import BTCE, BTCEPublic
  
subject: Add public imports to exchange module