Silent wrong shapes

[frostedoyster]

When calling Mops from C++ and implicitly initializing mops::Tensors,
something like
{O.data(), {1000}}
can silently initialize a 3D Mops tensor.

[Luthaf]

The problem is that the other two dimensions are initialized to 0, right? I don't think there is much we can do about this, it's how brace initialization works in C++. We might be able to define constructors that take the shape as three arguments, but I'm not sure how this would look like, since we would need to have different constructors for different values of the shape size template parameter.