Added doxygen comment for clsparseSpgemm API - precondition that csr matrices should have column indices of each row sorted
Added doxygen comment for clsparseSpgemm API - precondition that csr matrices should have column indices of each row sorted

kknox/clSPARSE,clMathLibraries/clSPARSE,jlgreathouse/clSPARSE,jpola/clSPARSE,kknox/clSPARSE,ghisvail/clSPARSE,ghisvail/clSPARSE,jlgreathouse/clSPARSE,kvaragan/clSPARSE,jpola/clSPARSE,kvaragan/clSPARSE,clMathLibraries/clSPARSE