add: api provide blocks by hash, id, head
add: api provide blocks by hash, id, head

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