Merge pull request #4 from ethers/pr

create and sign data-less transactions is now client-side
start using ethereumjs-lib
use ethereumjs-lib for creating and signing data-less transactions
implementation moved to ethereumjs-lib
fix applytx for PoC5

applytx interface was updated in pyethereum
  2a290a0cf6ff14f8ee569bc0880d6dab7581e3f7
mkContract and signing is now client-side