Define _GNU_SOURCE in the CFLAGS.
Update the README.
Remove the duplicate Gentoo init script ndhc.sh that is in the root.
Remove DESIGN -- it's outdated.
initialization. Fetching if/address/index/mac mappings is done only once at
program init, so it is done synchronously as an exception to this rule.
Rewrite the netlink handling. Now uses NIH code that should be safe, small,
and correct. No external deps FTW.
