Add clean target to makefile
Add clean target to makefile

People frequently expect this to exist, so they can remove compiled
files for packaging, etc.

karlstav/cava,jubalh/cava,nrhine1/cava,Suninus/cava,anko/cava,nikp123/cava,jubalh/cava,nikp123/cava,phijor/cava,phijor/cava,anko/cava,karlstav/cava,Suninus/cava,nrhine1/cava