TODO:
[ ] manual check memcpy bounds.
[ ] add flag (-s?) to probe a specific DHCP server, not broadcast?
    probably skip in run() Init: etc stages.
[ ] replace unsigned char ip[4] and so on from function declarations.
[?] ipv6 support ?

Changed (for now):
	- cleanup
		- code style.
		- trailing whitespace and use tabs.
		- remove debug (dbgprintf()) code in sdhcp.c.
		- code compiles more cleanly (ansi and c99),
		  -D_BSD_SOURCE added and explicitly added missing headers (time.h and unistd.h).
		- moved man page from sdhcp.8 to sdhcp.1
		- changed man page to mandoc.
	- typos:
		- sdhcp.c: interface typo.
		- sdhcp.1: shdcp typo.
	- replace write() for stdout messages with fprintf()
	- replace die() with eprintf().
	- makefile:
		- man page install should respect $DESTDIR.
		- make sure on install /sbin and mandir exists.
		- add config.mk, and follow suckless Makefile style.
	- add arg.h
		- first parameter remains interface.
		- second parameter is optional client-id, used to be hardcoded to
		  "vaio".
		- add -d flag, don't update /etc/resolv.conf.
		- add -i flag, don't set ip.
		- add -f flag, run in foreground.
		- add -e flag, run program, this has the following variables set:
		  $SERVER, DHCP ip.
		  $DNS, DNS ip.
		  $ROUTER, router ip.
		  $MASK, network mask.
		  $CLIENT, client ip.