We need implementations and dispatching logic for the following precompiles

Introduced in Homestead:

• 0x1 ecrecover
• 0x2 sha256
• 0x3 ripemd160
• 0x4 identity

Introduced in Byzantium:

• 0x5 modexp
• 0x6 ecadd
• 0x7 ecmul
• 0x8 ecpairing

Reference implementations:
https://github.com/ethereum/py-evm/tree/master/eth/precompiles