Come up with a release procedure

As the source code is based on isc-dhcp, the natural choice would be to reuse make dist. However, there are couple things that are not covered:

• web interface (the whole web/ dir)
• python tests
• much of the new documentation
• much of the code was removed

Also, this might be a good time to remove remaining legacy code (the server in particular). Initially, the server was left over as possibly an assistance for testing migration. But right now I think it's more of a nuisance. Users might incorrectly perceive this as some kind of extended life of isc-dhcpd...