Change binary representations to hexadecimal from binary

[hannes-steffenhagen-diffblue]

As of the merging of this PR, bitvectors in CBMC are now represented as hexadecimal, so we need to update our bitvector generation (Uint_To_Binary and Ureal_To_Binary in particular) to produce a hex representation. Could be most easily achieved by simply taking the existing *_To_Binary functions and wrapping them with a Binary_To_Hex function.