Hi guys!

I need to make a function that multiplies an arbitrary number of matrices. My current attempt is the following:

```
@inline function compose_rotation(D1::Matrix, Ds::Matrix...)
for Di in Ds
D1 = Di*D1
end
D1
end
```

The problem is that the performance is much worse than only the multiplication:

```
D1 = rand(3,3)
D2 = rand(3,3)
@time for i=1:10000000
compose_rotation(D1,D2,D1,D2)
end
2.406881 seconds (30.00 M allocations: 4.470 GiB, 1.90% gc time)
@time for i=1:10000000
D1*D2*D1*D2
end
2.004193 seconds (30.00 M allocations: 4.470 GiB, 2.44% gc time)
```

I am wondering: since I will always know how many matrices it is necessary to multiply at compile time, is there any way to “unroll” to loop so that I can improve the performance?

P.S.: This seems a little silly, but this function will be used to compute a composed rotation regardless the choice of the rotation description (matrix, quaternion, Euler axis/angle, etc.).