Document thrust::pointer in thrust/memory.h
Document thrust::pointer in thrust/memory.h

Fixes issue 440

h1arshad/thrust,Vishwa07/thrust,allendaicool/thrust,UIKit0/thrust,hemmingway/thrust,lishi0927/thrust,malenie/thrust,malenie/thrust,allendaicool/thrust,UIKit0/thrust,Vishwa07/thrust,julianromera/thrust,google-code-export/thrust,rdmenezes/thrust,allendaicool/thrust,hemmingway/thrust,lishi0927/thrust,UIKit0/thrust,allendaicool/thrust,levendlee/thrust,malenie/thrust,UIKit0/thrust,h1arshad/thrust,bfurtaw/thrust,rdmenezes/thrust,rdmenezes/thrust,lishi0927/thrust,hemmingway/thrust,rdmenezes/thrust,google-code-export/thrust,Vishwa07/thrust,bfurtaw/thrust,google-code-export/thrust,h1arshad/thrust,levendlee/thrust,julianromera/thrust,bfurtaw/thrust,Vishwa07/thrust,bfurtaw/thrust,levendlee/thrust,julianromera/thrust,hemmingway/thrust,google-code-export/thrust,h1arshad/thrust,levendlee/thrust,malenie/thrust,julianromera/thrust,lishi0927/thrust