change typedef to using according to preferred coding style
change typedef to using according to preferred coding style

ruchevits/solidity,chriseth/solidity-doc-test,douglas-larocca/solidity,ruchevits/solidity,LefterisJP/solidity,ruchevits/solidity,vaporry/solidity,LianaHus/solidity,shahankhatch/solidity,debris/solidity,arkpar/solidity,ethers/solidity,ruchevits/solidity,gluk256/solidity,chriseth/solidity