Add new Ipaddr_cstruct and Macaddr_cstruct libraries

[avsm]

for conversion to/from cstructs

based on #36

Co-authored-by: Nicolás Ojeda Bär n.oje.bar@gmail.com

[hannesm]

this looks good to me, the only nit I have is: could we add an optional ?off:int argument to the functions so we can read&write at offsets other than 0? (otoh, cstructs can be shift/split to the right position)

[avsm]

It simplifies it a lot without the offset argument, and I also figured that cstruct is designed to have efficient shift/splits (with only OCaml minor heap allocation). So I'd prefer to leave it this way rather than repeating elements of the Cstruct interface here unless you strongly prefer to have it.

[avsm]

I'll go ahead and release this, on the basis that adding ?off later is just adding an optional label and so not a huge interface change...