Any particular reason for the dot product of two tuples to be undefined (v0.6)? Similarly for `norm`

, or `cross`

.

```
julia> dot((1, 3, 2), (1, 3, 2))
ERROR: MethodError: no method matching dot(::Tuple{Int64,Int64}, ::Tuple{Int64,Int64})
```

This is potential useful in many applications.