The copyright and license notice is already in the LICENSE file. There
is no justifiable reason to also require that it be included in every
file, since the individual files are not individually distributed except
as part of the entire package.
These are options needed for real-world multicasting.
Implementation notes:
- POSIX only.
- IPv4 only (IPv6 multicast is a tricky beast).
- Didn't update tests, because it can't effectively be demonstrated on
localhost only.