[dwm] nmaster, clientspertag and tilecols for dwm-4.6

[pancake]

I have ported tilecols and clientspertag on top of the nmaster patch.

You can read the documentation here:

  http://news.nopcode.org/nmaster.c

Wiki pages are updated too.

Have fun :)

PD: Arg, for me dwm 4.6 looks perfect for a relase

  --pancake