This PR implements `Std.Net.Addr` which contains structures around IP
and socket addresses.
While we could implement our own parser instead of going through the
`addr_in`/`addr_in6` route we will need to implement these conversions
to make proper system calls anyway. Hence this is likely the approach
with the least amount of non trivial code overall. The only thing I am
uncertain about is whether `ofString` should return `Option` or
`Except`, unfortunately `libuv` doesn't hand out error messages on IP
parsing.
