Add support for hex literals

[stefandeml]

Would be nice to have some support for hex literals to make declarations like the following less verbose: field[32] h0 = [0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1] could be something like: field[32] h0 = hex!("0x6a09e667")

[Schaeff]

Can this wait for integer types?