CODESIZE and EXTCODESIZE

[JoranHonig]

Description

CODESIZE uses the number of instructions versus their actual size. EXTCODESIZE doesn't use a concrete number atm which it should.
@LoCorVin reported muellerberndt/laser-ethereum#41 in the laser repository.

implementation
To fix this problem both modules will need some way of accessing the bytecode of a contract to calculate the size in bytes, or some way to access it directly. And have the instruction implementation use that value