[dwm] tags definition

I was too tired of defining 4 different keys for each tag inside
config.h, so I created a TAGKEYS macro. I vote for its inclusion in
main dwm. I was thinking about having the (uint[]){ 1 << Tag} inside
the macro, or even (uint[]){ 1 << (Key - 1)} , but since it is in
config.h all that is up to you and I think this is the most "standard"
way (the idea is having some consistency with the other key
definitions).

Attached is a modified config.def.h, I hope you like it,

-- 
- yiyus || JGL .