add constructor for a dimension pair, make applylayers return self if no layers
add constructor for a dimension pair, make applylayers return self if no layers

sightmachine/SimpleCV2,beni55/SimpleCV,beni55/SimpleCV,jyt109/SimpleCV,hayd/SimpleCV,gskielian/SimpleCV,sightmachine/SimpleCV2,jayrambhia/SimpleCV2,hurdlea/SimpleCV,onaclovtech/SimpleCV,hayd/SimpleCV,beni55/SimpleCV,nikhilgk/SimpleCV,jyt109/SimpleCV,beni55/SimpleCV,tpltnt/SimpleCV,sightmachine/SimpleCV,nikhilgk/SimpleCV,onaclovtech/SimpleCV,onaclovtech/SimpleCV,jyt109/SimpleCV,onaclovtech/SimpleCV,gskielian/SimpleCV,jyt109/SimpleCV,onaclovtech/SimpleCV,nils-werner/SimpleCV,jayrambhia/SimpleCV2,nils-werner/SimpleCV,gskielian/SimpleCV,nikhilgk/SimpleCV,hayd/SimpleCV,hurdlea/SimpleCV,gskielian/SimpleCV,tpltnt/SimpleCV,tpltnt/SimpleCV,nils-werner/SimpleCV,hayd/SimpleCV,jlegendary/SimpleCV,jlegendary/SimpleCV,jayrambhia/SimpleCV2,hurdlea/SimpleCV,jlegendary/SimpleCV,nikhilgk/SimpleCV,gskielian/SimpleCV,sightmachine/SimpleCV2,jyt109/SimpleCV,hurdlea/SimpleCV,jlegendary/SimpleCV,sightmachine/SimpleCV,sightmachine/SimpleCV,hayd/SimpleCV,jayrambhia/SimpleCV2,sightmachine/SimpleCV2,beni55/SimpleCV,nils-werner/SimpleCV,sightmachine/SimpleCV,tpltnt/SimpleCV,jlegendary/SimpleCV,sightmachine/SimpleCV,nikhilgk/SimpleCV,tpltnt/SimpleCV,hurdlea/SimpleCV,nils-werner/SimpleCV