Compute and memory operations

# Keccak Op
KECCAK = 0x20

# Environmental Ops
CALLDATACOPY = 0x37
CODECOPY = 0x39
RETURNDATACOPY = 0x3E

# Memory Operations
MLOAD = 0x51
MSTORE = 0x52
MSTORE8 = 0x53
MCOPY = 0x5E

# System Operations
RETURN = 0xF3
REVERT = 0xFD