add: convenience methods
add: convenience methods

inzem77/pyethereum,shahankhatch/pyethereum,vaporry/pyethereum,ebuchman/daoist_protocol,pipermerriam/pyethereum,pipermerriam/pyethereum,ethermarket/pyethereum,ethereum/pyethereum,holiman/pyethereum,shahankhatch/pyethereum,ckeenan/pyethereum,harlantwood/pyethereum,karlfloersch/pyethereum,jnnk/pyethereum,karlfloersch/pyethereum,ethers/pyethereum,ebuchman/daoist_protocol,ddworken/pyethereum,ethereum/pyethereum