Add a [Ipaddr_unix] module to convert to-and-from the standard library.
Add a toplevel prettyprinter in the `ipaddr.top` package
Make building the Unix library optional, but on by default
Standardize and correct Ipaddr_unix docs
Standardize and correct Ipaddr docs; add missing Ipaddr.Prefix.pp_hum
Add missing Ipaddr.Prefix and Opaddr.V6.Prefix printers
Mark as OCaml 4+ only for Travis and update README
Retain 3.12 support by adding ocaml-compiler-libs install; doc it
bring back 3.12 support
build 3.12 with travis, clarify README
Merge pull request #24 from mirage/unix-support

Unix support and Top Level printers