[dwm] CLI color/font override pull request

Hi All,
Eager to avoid the excessive recompiling of dwm on a 433mhz proc(takes
~25seconds), I sought to pull request dwm to support "-fn" and other appearance
changes.
I've attached two pull requestes, one for dwm.c and one for config.def.h.
The code I put together is based heavily off dmenu's arg processing and adds
a little more than thirty SLOCs.
The pull request for config.def.h adds no SLOCs.
Best,

--
Ian Daniher