Genesis extra-data encoder and decoder library for Istanbul consensus.
Istanbul tools is used to generate extra-data field of genesis due to extra-data is combined signer vanity with RLP encoded `Istanbul extra data`. The `Istanbul extra data` struct is defined as follows:
Encoded Istanbul extra-data: 0x0000000000000000000000000000000000000000000000000000000000000000f89af85494475cc98b5521ab2a1335683e7567c8048bfe79ed9407d8299de61faed3686ba4c4e6c3b9083d7e2371944fe035ce99af680d89e2c4d73aca01dbfc1bd2fd94dc421209441a754f79c4a4ecd2b49c935aad0312b8410000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000c0