Make more extensive use of Bap_c

[bmourad01]

Per discussion with @ivg on #167, the C frontend could re-use a lot of the functionality provided in this library. Indeed, we've switched to using Bap_c.Std.Data.model for capturing the correct sizes of integers based on the target. If we seek to extend our datatype support in the frontend, perhaps we don't need to reinvent the wheel, as this library gives us a lot of the tools we need.