Add method for Ac_mat_B(Matrix,Vector)

Before:
```julia
julia> mX=randn(1000000,40);mY=randn(1000000);

julia> @elapsed mX'mY
0.6670470237731934

julia> @elapsed mX'mY
0.5422990322113037
```
After:
```julia
julia> mX=randn(1000000,40);mY=randn(1000000);

julia> @elapsed mX'mY
0.19115304946899414

julia> @elapsed mX'mY
0.11007881164550781