feature request findmax(A,dims)

getting the maximum and its location in one pass is very useful. at current it's not supported along dimension `d` of an array. 

```
A = rand(3,3,3)
now = mapslices(findmax,A,3)
#or
for i in 1:3
    for j in 1:3
         now[i,j] = findmax(A[i,j,:])
    end
end
then = findmax(A,3)
```

it's odd to have 

```
max(A,dims)
```

and not `findmax(A,dims)`
