EIP-86 update

[arkpar]

A few minor changes to EIP-86 have been clarified/introduced recently.

1. New contract address gets generated from code hash for contracts created with create transactions only. CREATE instruction retains old behaviour (address generated from sender and nonce).
2. Contract can be created even if existing account is non-empty (has balance). The only requirement is that the code does not exist.
3. CREATE_P2SH renamed to CREATE2

[gavofyork]

even now, a contract can be created at an address that exists (with a non-zero balance or even code - though the latter is practically impossible).