Provide several simple fixed-sized hash data type and their static constructors.

Example

use ckb_fixed_hash::{H256, h256};

const N1: H256 = h256!("0xffffffff_ffffffff_ffffffff_fffffffe_baaedce6_af48a03b_bfd25e8c_d0364141");
const N2: H256 = H256([
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xfe, 0xba, 0xae, 0xdc, 0xe6, 0xaf, 0x48, 0xa0, 0x3b, 0xbf, 0xd2, 0x5e, 0x8c, 0xd0, 0x36,
0x41, 0x41
]);
assert_eq!(N1, N2);

const ONE1: H256 = h256!("0x1");
const ONE2: H256 = H256([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]);
assert_eq!(ONE1, ONE2);