[dwm] start maximized patch

This is my very first patch.
And my very first post on the list! :)
The patch allows ppl to have chosen window class start maximized.

I have a tag for almost every program I use, so I can always go full
screen. Some program does not save his size on exit (ex. xterm),
so every time it starts I have to maximize the window.
Thats frustrating when you start lots of programs with a startup script.

With this patch, Rule struct gets a "ismaxed" bool which can be set to
true/false through config.h. Quite simple.

Wyrmskull