updated sparse matrix-matrix multiply to use thrust::reduce_by_key
updated sparse matrix-matrix multiply to use thrust::reduce_by_key

vkirangoud/cusp-library,vkirangoud/cusp-library,victordion/cusp-library,gshashidhar125/cusp-library,baiyunping333/cusp-library,vkirangoud/cusp-library,baiyunping333/cusp-library,gshashidhar125/cusp-library,baiyunping333/cusp-library,tectronics/cusp-library,gshashidhar125/cusp-library,victordion/cusp-library,victordion/cusp-library,victordion/cusp-library,tectronics/cusp-library,tectronics/cusp-library,tectronics/cusp-library,baiyunping333/cusp-library,gshashidhar125/cusp-library,vkirangoud/cusp-library